From 07182fad27af86f254612474932cc8fab49946db Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Sun, 28 Jul 2024 20:21:15 +0500
Subject: [PATCH 01/17] initial commit

---
 exercise1/problem1/main.go | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/exercise1/problem1/main.go b/exercise1/problem1/main.go
index dfca465c..e1a52439 100644
--- a/exercise1/problem1/main.go
+++ b/exercise1/problem1/main.go
@@ -1,3 +1,8 @@
 package main
 
-func addUp() {}
+func addUp(n int) (sum int) {
+	for i := 0; i <= n; i++ {
+		sum += i
+	}
+	return
+}

From 92b3c04594abe4f64d9ec17364ad46bdc0826a05 Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Mon, 29 Jul 2024 16:55:16 +0500
Subject: [PATCH 02/17] completed

---
 exercise1/problem10/main.go | 21 ++++++++++++++++++++-
 exercise1/problem2/main.go  | 15 ++++++++++++++-
 exercise1/problem3/main.go  |  8 +++++++-
 exercise1/problem4/main.go  | 13 ++++++++++++-
 exercise1/problem5/main.go  |  6 +++++-
 exercise1/problem6/main.go  | 18 +++++++++++++++++-
 exercise1/problem7/main.go  | 10 +++++++++-
 exercise1/problem8/main.go  | 10 +++++++++-
 exercise1/problem9/main.go  | 12 +++++++++---
 9 files changed, 102 insertions(+), 11 deletions(-)

diff --git a/exercise1/problem10/main.go b/exercise1/problem10/main.go
index 04ec3430..a707031d 100644
--- a/exercise1/problem10/main.go
+++ b/exercise1/problem10/main.go
@@ -1,3 +1,22 @@
 package main
 
-func sum() {}
+import (
+	"fmt"
+	"strconv"
+)
+
+func sum(m, n string) (string, error) {
+	intM, err := strconv.Atoi(m)
+	if err != nil {
+		return "", fmt.Errorf("string: %s cannot be converted", m)
+	}
+
+	intN, err := strconv.Atoi(n)
+	if err != nil {
+		return "", fmt.Errorf("string: %s cannot be converted", n)
+	}
+
+	result := intM + intN
+
+	return strconv.Itoa(result), nil
+}
diff --git a/exercise1/problem2/main.go b/exercise1/problem2/main.go
index 2ca540b8..fe75619c 100644
--- a/exercise1/problem2/main.go
+++ b/exercise1/problem2/main.go
@@ -1,3 +1,16 @@
 package main
 
-func binary() {}
+import "strconv"
+
+func binary(n int) (binaryStr string) {
+	if n == 0 {
+		return "0"
+	}
+
+	for n > 0 {
+		binaryStr = strconv.Itoa(n%2) + binaryStr
+		n /= 2
+	}
+
+	return
+}
diff --git a/exercise1/problem3/main.go b/exercise1/problem3/main.go
index d346641a..c7d52ff0 100644
--- a/exercise1/problem3/main.go
+++ b/exercise1/problem3/main.go
@@ -1,3 +1,9 @@
 package main
 
-func numberSquares() {}
+func numberSquares(n int) int {
+	sum := 0
+	for i := 1; i <= n; i++ {
+		sum += i * i
+	}
+	return sum
+}
diff --git a/exercise1/problem4/main.go b/exercise1/problem4/main.go
index 74af9044..7a13f7da 100644
--- a/exercise1/problem4/main.go
+++ b/exercise1/problem4/main.go
@@ -1,3 +1,14 @@
 package main
 
-func detectWord() {}
+import (
+	"unicode"
+)
+
+func detectWord(word string) (detectWord string) {
+	for _, char := range word {
+		if unicode.IsLower(char) {
+			detectWord += string(char)
+		}
+	}
+	return
+}
diff --git a/exercise1/problem5/main.go b/exercise1/problem5/main.go
index c5a804c9..eb4cd0a6 100644
--- a/exercise1/problem5/main.go
+++ b/exercise1/problem5/main.go
@@ -1,3 +1,7 @@
 package main
 
-func potatoes() {}
+import "strings"
+
+func potatoes(word string) int {
+	return strings.Count(word, "potato")
+}
diff --git a/exercise1/problem6/main.go b/exercise1/problem6/main.go
index 06043890..eb87a9c5 100644
--- a/exercise1/problem6/main.go
+++ b/exercise1/problem6/main.go
@@ -1,3 +1,19 @@
 package main
 
-func emojify() {}
+import "strings"
+
+func emojify(word string) string {
+	if strings.Contains(word, "smile") {
+		word = strings.ReplaceAll(word, "smile", "🙂")
+	}
+	if strings.Contains(word, "grin") {
+		word = strings.ReplaceAll(word, "grin", "😀")
+	}
+	if strings.Contains(word, "sad") {
+		word = strings.ReplaceAll(word, "sad", "😥")
+	}
+	if strings.Contains(word, "mad") {
+		word = strings.ReplaceAll(word, "mad", "😠")
+	}
+	return word
+}
diff --git a/exercise1/problem7/main.go b/exercise1/problem7/main.go
index 57c99b5c..addb6313 100644
--- a/exercise1/problem7/main.go
+++ b/exercise1/problem7/main.go
@@ -1,3 +1,11 @@
 package main
 
-func highestDigit() {}
+func highestDigit(n int) (maxDigit int) {
+	for n > 0 {
+		if n%10 > maxDigit {
+			maxDigit = n % 10
+		}
+		n /= 10
+	}
+	return
+}
diff --git a/exercise1/problem8/main.go b/exercise1/problem8/main.go
index 97fa0dae..ac7d7229 100644
--- a/exercise1/problem8/main.go
+++ b/exercise1/problem8/main.go
@@ -1,3 +1,11 @@
 package main
 
-func countVowels() {}
+func countVowels(word string) (count int) {
+	for _, r := range word {
+		switch r {
+		case 'a', 'e', 'i', 'o', 'u':
+			count++
+		}
+	}
+	return
+}
diff --git a/exercise1/problem9/main.go b/exercise1/problem9/main.go
index e8c84a54..7aa6e484 100644
--- a/exercise1/problem9/main.go
+++ b/exercise1/problem9/main.go
@@ -1,7 +1,13 @@
 package main
 
-func bitwiseAND() {}
+func bitwiseAND(n, m int) int {
+	return n & m
+}
 
-func bitwiseOR() {}
+func bitwiseOR(n, m int) int {
+	return n | m
+}
 
-func bitwiseXOR() {}
+func bitwiseXOR(n, m int) int {
+	return n ^ m
+}

From 1b42660b1136dfd25961f74c4d67b96e4addbabb Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Fri, 27 Sep 2024 02:49:23 +0500
Subject: [PATCH 03/17] completed ex2

---
 exercise2/problem1/problem1.go   | 10 +++++++++-
 exercise2/problem10/problem10.go | 10 +++++++++-
 exercise2/problem11/problem11.go | 12 +++++++++++-
 exercise2/problem12/problem12.go | 10 +++++++++-
 exercise2/problem2/problem2.go   | 12 +++++++++++-
 exercise2/problem3/problem3.go   | 20 +++++++++++++++++++-
 exercise2/problem4/problem4.go   |  9 ++++++++-
 exercise2/problem5/problem5.go   | 16 +++++++++++++++-
 exercise2/problem6/problem6.go   | 10 +++++++++-
 exercise2/problem7/problem7.go   |  3 ++-
 exercise2/problem8/problem8.go   | 13 +++++--------
 exercise2/problem9/problem9.go   | 12 +++++++++++-
 12 files changed, 118 insertions(+), 19 deletions(-)

diff --git a/exercise2/problem1/problem1.go b/exercise2/problem1/problem1.go
index 4763006c..a7a885f6 100644
--- a/exercise2/problem1/problem1.go
+++ b/exercise2/problem1/problem1.go
@@ -1,4 +1,12 @@
 package problem1
 
-func isChangeEnough() {
+func isChangeEnough(changes [4]int, total float32) bool {
+	coinValues := [4]float32{0.25, 0.10, 0.05, 0.01}
+	var dollars float32
+
+	for i, coin := range changes {
+		dollars += float32(coin) * coinValues[i]
+	}
+
+	return dollars >= total
 }
diff --git a/exercise2/problem10/problem10.go b/exercise2/problem10/problem10.go
index 7142a022..cde772a1 100644
--- a/exercise2/problem10/problem10.go
+++ b/exercise2/problem10/problem10.go
@@ -1,3 +1,11 @@
 package problem10
 
-func factory() {}
+func factory() (map[string]int, func(string) func(int)) {
+	brandInfo := make(map[string]int)
+	return brandInfo, func(brandName string) func(int) {
+		brandInfo[brandName] = 0
+		return func(incrementValue int) {
+			brandInfo[brandName] += incrementValue
+		}
+	}
+}
diff --git a/exercise2/problem11/problem11.go b/exercise2/problem11/problem11.go
index 33988711..9cbee8cd 100644
--- a/exercise2/problem11/problem11.go
+++ b/exercise2/problem11/problem11.go
@@ -1,3 +1,13 @@
 package problem11
 
-func removeDups() {}
+func removeDups[T comparable](slice []T) []T {
+	result := []T{}
+	seen := make(map[T]struct{})
+	for _, value := range slice {
+		if _, ok := seen[value]; !ok {
+			seen[value] = struct{}{}
+			result = append(result, value)
+		}
+	}
+	return result
+}
diff --git a/exercise2/problem12/problem12.go b/exercise2/problem12/problem12.go
index 4c1ae327..b2933886 100644
--- a/exercise2/problem12/problem12.go
+++ b/exercise2/problem12/problem12.go
@@ -1,3 +1,11 @@
 package problem11
 
-func keysAndValues() {}
+func keysAndValues[K comparable, V comparable](inp map[K]V) ([]K, []V) {
+	keys := []K{}
+	values := []V{}
+	for key, value := range inp {
+		keys = append(keys, key)
+		values = append(values, value)
+	}
+	return keys, values
+}
diff --git a/exercise2/problem2/problem2.go b/exercise2/problem2/problem2.go
index fdb199f0..c2a429a0 100644
--- a/exercise2/problem2/problem2.go
+++ b/exercise2/problem2/problem2.go
@@ -1,4 +1,14 @@
 package problem2
 
-func capitalize() {
+import (
+	"strings"
+)
+
+func capitalize(names []string) []string {
+	for i, name := range names {
+		if len(name) > 0 {
+			names[i] = strings.ToUpper(string(name[0])) + strings.ToLower(name[1:])
+		}
+	}
+	return names
 }
diff --git a/exercise2/problem3/problem3.go b/exercise2/problem3/problem3.go
index f183fafb..3d41a5fd 100644
--- a/exercise2/problem3/problem3.go
+++ b/exercise2/problem3/problem3.go
@@ -9,5 +9,23 @@ const (
 	lr dir = "lr"
 )
 
-func diagonalize() {
+func diagonalize(n int, d dir) [][]int {
+	exp := make([][]int, n)
+
+	for i := 0; i < n; i++ {
+		exp[i] = make([]int, n)
+		for j := 0; j < n; j++ {
+			switch d {
+			case "ul":
+				exp[i][j] = i + j
+			case "ll":
+				exp[i][j] = n - i + j - 1
+			case "ur":
+				exp[i][j] = n + i - j - 1
+			case "lr":
+				exp[i][j] = (n - i - 1) + (n - j - 1)
+			}
+		}
+	}
+	return exp
 }
diff --git a/exercise2/problem4/problem4.go b/exercise2/problem4/problem4.go
index 1f680a4d..d79ffdcc 100644
--- a/exercise2/problem4/problem4.go
+++ b/exercise2/problem4/problem4.go
@@ -1,4 +1,11 @@
 package problem4
 
-func mapping() {
+import "strings"
+
+func mapping(inp []string) map[string]string {
+	exp := make(map[string]string)
+	for _, value := range inp {
+		exp[value] = strings.ToUpper(value)
+	}
+	return exp
 }
diff --git a/exercise2/problem5/problem5.go b/exercise2/problem5/problem5.go
index 43fb96a4..3620d1fc 100644
--- a/exercise2/problem5/problem5.go
+++ b/exercise2/problem5/problem5.go
@@ -1,4 +1,18 @@
 package problem5
 
-func products() {
+import "sort"
+
+func products(catalog map[string]int, minPrice int) (exp []string) {
+	for product, price := range catalog {
+		if price >= minPrice {
+			exp = append(exp, product)
+		}
+	}
+	sort.Slice(exp, func(i, j int) bool {
+		if catalog[exp[i]] == catalog[exp[j]] {
+			return exp[i] < exp[j]
+		}
+		return catalog[exp[i]] > catalog[exp[j]]
+	})
+	return
 }
diff --git a/exercise2/problem6/problem6.go b/exercise2/problem6/problem6.go
index 89fc5bfe..4fcf4194 100644
--- a/exercise2/problem6/problem6.go
+++ b/exercise2/problem6/problem6.go
@@ -1,4 +1,12 @@
 package problem6
 
-func sumOfTwo() {
+func sumOfTwo(a, b []int, sum int) bool {
+	for _, i := range a {
+		for _, j := range b {
+			if i+j == sum {
+				return true
+			}
+		}
+	}
+	return false
 }
diff --git a/exercise2/problem7/problem7.go b/exercise2/problem7/problem7.go
index 32514209..79f51068 100644
--- a/exercise2/problem7/problem7.go
+++ b/exercise2/problem7/problem7.go
@@ -1,4 +1,5 @@
 package problem7
 
-func swap() {
+func swap(a, b *int) {
+	*a, *b = *b, *a
 }
diff --git a/exercise2/problem8/problem8.go b/exercise2/problem8/problem8.go
index 9389d3b0..b28a0682 100644
--- a/exercise2/problem8/problem8.go
+++ b/exercise2/problem8/problem8.go
@@ -1,16 +1,13 @@
 package problem8
 
 func simplify(list []string) map[string]int {
-	var indMap map[string]int
-
-	indMap = make(map[string]int)
-	load(&indMap, &list)
-
+	indMap := make(map[string]int)
+	load(indMap, list)
 	return indMap
 }
 
-func load(m *map[string]int, students *[]string) {
-	for i, name := range *students {
-		(*m)[name] = i
+func load(m map[string]int, students []string) {
+	for i, name := range students {
+		m[name] = i
 	}
 }
diff --git a/exercise2/problem9/problem9.go b/exercise2/problem9/problem9.go
index fc96d21a..6d787ac4 100644
--- a/exercise2/problem9/problem9.go
+++ b/exercise2/problem9/problem9.go
@@ -1,3 +1,13 @@
 package problem9
 
-func factory() {}
+type resultType func(...int) []int
+
+func factory(multiple int) resultType {
+	return func(list ...int) []int {
+		result := make([]int, len(list))
+		for i, value := range list {
+			result[i] = value * multiple
+		}
+		return result
+	}
+}

From 34b616a580f51d9624992f1895dd9d857e1c9867 Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Fri, 27 Sep 2024 03:00:03 +0500
Subject: [PATCH 04/17] refactored

---
 exercise2/problem11/problem11.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/exercise2/problem11/problem11.go b/exercise2/problem11/problem11.go
index 9cbee8cd..66aa7860 100644
--- a/exercise2/problem11/problem11.go
+++ b/exercise2/problem11/problem11.go
@@ -2,7 +2,7 @@ package problem11
 
 func removeDups[T comparable](slice []T) []T {
 	result := []T{}
-	seen := make(map[T]struct{})
+	seen := map[T]struct{}{}
 	for _, value := range slice {
 		if _, ok := seen[value]; !ok {
 			seen[value] = struct{}{}

From 52367f9c6ab6f90966df13484bee16c7c904aa1b Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Wed, 2 Oct 2024 21:24:23 +0500
Subject: [PATCH 05/17] WIP

---
 exercise3/problem1/problem1.go | 34 ++++++++++++++++++++++++++++++++-
 exercise3/problem2/problem2.go | 35 +++++++++++++++++++++++++++++++++-
 exercise3/problem3/problem3.go |  5 +++++
 3 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/exercise3/problem1/problem1.go b/exercise3/problem1/problem1.go
index d45605c6..1011ad35 100644
--- a/exercise3/problem1/problem1.go
+++ b/exercise3/problem1/problem1.go
@@ -1,3 +1,35 @@
 package problem1
 
-type Queue struct{}
+import "errors"
+
+type Queue struct {
+	items []interface{}
+}
+
+func (q *Queue) Enqueue(item interface{}) {
+	q.items = append(q.items, item)
+}
+
+func (q *Queue) Dequeue() (interface{}, error) {
+	if q.IsEmpty() {
+		return nil, errors.New("Queue is empty")
+	}
+	item := q.items[0]
+	q.items = q.items[1:]
+	return item, nil
+}
+
+func (q *Queue) Peek() (interface{}, error) {
+	if q.IsEmpty() {
+		return nil, errors.New("Queue is empty")
+	}
+	return q.items[0], nil
+}
+
+func (q *Queue) Size() int {
+	return len(q.items)
+}
+
+func (q *Queue) IsEmpty() bool {
+	return len(q.items) == 0
+}
diff --git a/exercise3/problem2/problem2.go b/exercise3/problem2/problem2.go
index e9059889..4cb503c6 100644
--- a/exercise3/problem2/problem2.go
+++ b/exercise3/problem2/problem2.go
@@ -1,3 +1,36 @@
 package problem2
 
-type Stack struct{}
+import "errors"
+
+type Stack struct {
+	items []interface{}
+}
+
+func (s *Stack) Push(item interface{}) {
+	s.items = append(s.items, item)
+}
+
+func (s *Stack) Pop() (interface{}, error) {
+	if s.IsEmpty() {
+		return nil, errors.New("Stack is empty")
+	}
+	lastIndex := s.Size() - 1
+	item := s.items[lastIndex]
+	s.items = s.items[:lastIndex]
+	return item, nil
+}
+
+func (s *Stack) Peek() (interface{}, error) {
+	if s.IsEmpty() {
+		return nil, errors.New("Stack is empty")
+	}
+	return s.items[s.Size()-1], nil
+}
+
+func (s *Stack) Size() int {
+	return len(s.items)
+}
+
+func (s *Stack) IsEmpty() bool {
+	return s.Size() == 0
+}
diff --git a/exercise3/problem3/problem3.go b/exercise3/problem3/problem3.go
index d8d79ac0..97fb4028 100644
--- a/exercise3/problem3/problem3.go
+++ b/exercise3/problem3/problem3.go
@@ -1,3 +1,8 @@
 package problem3
 
 type Set struct{}
+
+func NewSet() *Set {
+
+	return &Set{}
+}

From 11b274223f180fabb34209d81d596ef1a860ead5 Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Sat, 5 Oct 2024 17:35:48 +0500
Subject: [PATCH 06/17] ready for review

---
 .vscode/launch.json            |  15 ++++
 .vscode/settings.json          |  22 ++++++
 exercise3/problem3/problem3.go | 102 ++++++++++++++++++++++++-
 exercise3/problem4/problem4.go | 131 ++++++++++++++++++++++++++++++++-
 exercise3/problem5/problem5.go |  19 ++++-
 exercise3/problem6/problem6.go |  30 +++++++-
 exercise3/problem7/problem7.go |  44 +++++++++++
 7 files changed, 356 insertions(+), 7 deletions(-)
 create mode 100644 .vscode/launch.json
 create mode 100644 .vscode/settings.json

diff --git a/.vscode/launch.json b/.vscode/launch.json
new file mode 100644
index 00000000..608d3c69
--- /dev/null
+++ b/.vscode/launch.json
@@ -0,0 +1,15 @@
+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Launch Package",
+            "type": "go",
+            "request": "launch",
+            "mode": "auto",
+            "program": "${fileDirname}"
+        }
+    ]
+}
\ No newline at end of file
diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 00000000..4fe3b603
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,22 @@
+{
+    "workbench.colorCustomizations": {
+        "activityBar.activeBackground": "#fa1b49",
+        "activityBar.background": "#fa1b49",
+        "activityBar.foreground": "#e7e7e7",
+        "activityBar.inactiveForeground": "#e7e7e799",
+        "activityBarBadge.background": "#155e02",
+        "activityBarBadge.foreground": "#e7e7e7",
+        "commandCenter.border": "#e7e7e799",
+        "sash.hoverBorder": "#fa1b49",
+        "statusBar.background": "#dd0531",
+        "statusBar.foreground": "#e7e7e7",
+        "statusBarItem.hoverBackground": "#fa1b49",
+        "statusBarItem.remoteBackground": "#dd0531",
+        "statusBarItem.remoteForeground": "#e7e7e7",
+        "titleBar.activeBackground": "#dd0531",
+        "titleBar.activeForeground": "#e7e7e7",
+        "titleBar.inactiveBackground": "#dd053199",
+        "titleBar.inactiveForeground": "#e7e7e799"
+    },
+    "peacock.color": "#dd0531"
+}
\ No newline at end of file
diff --git a/exercise3/problem3/problem3.go b/exercise3/problem3/problem3.go
index 97fb4028..a292d7df 100644
--- a/exercise3/problem3/problem3.go
+++ b/exercise3/problem3/problem3.go
@@ -1,8 +1,106 @@
 package problem3
 
-type Set struct{}
+type Set struct {
+	items map[interface{}]struct{}
+}
 
 func NewSet() *Set {
+	return &Set{
+		items: make(map[interface{}]struct{}),
+	}
+}
+
+func (s *Set) Add(item interface{}) {
+	s.items[item] = struct{}{}
+}
+
+func (s *Set) Remove(item interface{}) {
+	delete(s.items, item)
+}
+
+func (s *Set) IsEmpty() bool {
+	return len(s.items) == 0
+}
+
+func (s *Set) Size() int {
+	return len(s.items)
+}
+
+func (s *Set) Has(item interface{}) bool {
+	_, exists := s.items[item]
+	return exists
+}
+
+func (s *Set) Copy() *Set {
+	resultSet := NewSet()
+	for key := range s.items {
+		resultSet.Add(key)
+	}
+	return resultSet
+}
+
+func (s *Set) Difference(r *Set) *Set {
+	resultSet := NewSet()
+	for key := range s.items {
+		if !r.Has(key) {
+			resultSet.Add(key)
+		}
+	}
+	return resultSet
+}
+
+func (s *Set) IsSubset(r *Set) bool {
+	for key := range s.items {
+		if !r.Has(key) {
+			return false
+		}
+	}
+	return true
+}
+
+func (s *Set) List() []interface{} {
+	result := []interface{}{}
+	for key := range s.items {
+		result = append(result, key)
+	}
+	return result
+}
+
+func Union(sets ...*Set) *Set {
+	resultSet := NewSet()
+	for _, set := range sets {
+		for key := range set.items {
+			resultSet.Add(key)
+		}
+	}
+	return resultSet
+}
+
+func Intersect(sets ...*Set) *Set {
+	if len(sets) == 0 {
+		return NewSet()
+	}
+
+	minSet := sets[0]
+	for _, set := range sets[1:] {
+		if set.Size() < minSet.Size() {
+			minSet = set
+		}
+	}
+
+	resultSet := NewSet()
+	for key := range minSet.items {
+		isCommon := true
+		for _, set := range sets {
+			if !set.Has(key) {
+				isCommon = false
+				break
+			}
+		}
+		if isCommon {
+			resultSet.Add(key)
+		}
+	}
 
-	return &Set{}
+	return resultSet
 }
diff --git a/exercise3/problem4/problem4.go b/exercise3/problem4/problem4.go
index ebf78147..7ca4847f 100644
--- a/exercise3/problem4/problem4.go
+++ b/exercise3/problem4/problem4.go
@@ -1,3 +1,132 @@
 package problem4
 
-type LinkedList struct{}
+import (
+	"errors"
+)
+
+type Element[T comparable] struct {
+	value T
+	next  *Element[T]
+}
+
+type LinkedList[T comparable] struct {
+	head *Element[T]
+	tail *Element[T]
+	size int
+}
+
+func (l *LinkedList[T]) Add(e *Element[T]) {
+	if l.head == nil {
+		l.head = e
+		l.tail = e
+	} else {
+		l.tail.next = e
+		l.tail = e
+	}
+	l.size++
+}
+
+func (l *LinkedList[T]) Size() int {
+	return l.size
+}
+
+func (l *LinkedList[T]) Insert(e *Element[T], index int) error {
+	if index < 0 || index > l.size {
+		return errors.New("index out of range")
+	}
+
+	if index == 0 {
+		e.next = l.head
+		l.head = e
+		if l.size == 0 {
+			l.tail = e
+		}
+	} else {
+		prev, err := l.findPreviousByIndex(index - 1)
+		if err != nil {
+			return err
+		}
+		e.next = prev.next
+		prev.next = e
+		if e.next == nil {
+			l.tail = e
+		}
+	}
+	l.size++
+	return nil
+}
+
+func (l *LinkedList[T]) Delete(e *Element[T]) error {
+	if l.IsEmpty() {
+		return errors.New("linkedlist is empty")
+	}
+
+	if l.head.value == e.value {
+		l.head = l.head.next
+		if l.head == nil {
+			l.tail = nil
+		}
+	} else {
+		prev, err := l.findPrevious(e.value)
+		if err != nil {
+			return err
+		}
+		prev.next = prev.next.next
+		if prev.next == nil {
+			l.tail = prev
+		}
+	}
+	l.size--
+	return nil
+}
+
+func (l *LinkedList[T]) Find(value T) (*Element[T], error) {
+	current := l.head
+	for current != nil {
+		if current.value == value {
+			return current, nil
+		}
+		current = current.next
+	}
+	return nil, errors.New("value not found")
+}
+
+func (l *LinkedList[T]) List() []T {
+	result := make([]T, 0, l.size)
+	for current := l.head; current != nil; current = current.next {
+		result = append(result, current.value)
+	}
+	return result
+}
+
+func (l *LinkedList[T]) IsEmpty() bool {
+	return l.size == 0
+}
+
+func (l *LinkedList[T]) findPreviousByIndex(index int) (*Element[T], error) {
+	if index < 0 || index >= l.size {
+		return nil, errors.New("index out of range")
+	}
+
+	current := l.head
+	for i := 0; i < index; i++ {
+		current = current.next
+	}
+	return current, nil
+}
+
+func (l *LinkedList[T]) findPrevious(value T) (*Element[T], error) {
+	if l.head == nil || l.head.value == value {
+		return nil, errors.New("value not found")
+	}
+
+	current := l.head
+	for current.next != nil && current.next.value != value {
+		current = current.next
+	}
+
+	if current.next == nil {
+		return nil, errors.New("value not found")
+	}
+	return current, nil
+}
diff --git a/exercise3/problem5/problem5.go b/exercise3/problem5/problem5.go
index 4177599f..c490a487 100644
--- a/exercise3/problem5/problem5.go
+++ b/exercise3/problem5/problem5.go
@@ -1,3 +1,20 @@
 package problem5
 
-type Person struct{}
+import "fmt"
+
+type Person struct {
+	name string
+	age  int
+}
+
+func (me *Person) compareAge(other *Person) string {
+	if other.age > me.age {
+		return fmt.Sprintf("%s is older than me.", other.name)
+	}
+
+	if other.age < me.age {
+		return fmt.Sprintf("%s is younger than me.", other.name)
+	}
+
+	return fmt.Sprintf("%s is the same age as me.", other.name)
+}
diff --git a/exercise3/problem6/problem6.go b/exercise3/problem6/problem6.go
index 4e8d1af8..9a0fa6e5 100644
--- a/exercise3/problem6/problem6.go
+++ b/exercise3/problem6/problem6.go
@@ -1,7 +1,31 @@
 package problem6
 
-type Animal struct{}
+type Animal struct {
+	name    string
+	legsNum int
+}
 
-type Insect struct{}
+func (a *Animal) GetLegs() int {
+	return a.legsNum
+}
 
-func sumOfAllLegsNum() {}
+type Insect struct {
+	name    string
+	legsNum int
+}
+
+func (i *Insect) GetLegs() int {
+	return i.legsNum
+}
+
+type HasLegs interface {
+	GetLegs() int
+}
+
+func sumOfAllLegsNum(list ...HasLegs) int {
+	total := 0
+	for _, l := range list {
+		total += l.GetLegs()
+	}
+	return total
+}
diff --git a/exercise3/problem7/problem7.go b/exercise3/problem7/problem7.go
index 26887151..d1773d93 100644
--- a/exercise3/problem7/problem7.go
+++ b/exercise3/problem7/problem7.go
@@ -1,10 +1,54 @@
 package problem7
 
+import "fmt"
+
+type Treasury interface {
+	withdraw(int)
+}
+
+type Post interface {
+	sendTo(string)
+}
+
 type BankAccount struct {
+	name    string
+	balance int
+}
+
+func (b *BankAccount) withdraw(amount int) {
+	b.balance -= amount
 }
 
 type FedexAccount struct {
+	name     string
+	packages []string
+}
+
+func (f *FedexAccount) sendTo(name string) {
+	f.packages = append(f.packages, fmt.Sprintf("%s send package to %s", f.name, name))
 }
 
 type KazPostAccount struct {
+	name     string
+	balance  int
+	packages []string
+}
+
+func (k *KazPostAccount) withdraw(amount int) {
+	k.balance -= amount
+}
+
+func (k *KazPostAccount) sendTo(name string) {
+	k.packages = append(k.packages, fmt.Sprintf("%s send package to %s", k.name, name))
+}
+
+func withdrawMoney(amount int, accounts ...Treasury) {
+	for _, account := range accounts {
+		account.withdraw(amount)
+	}
+}
+func sendPackagesTo(name string, posts ...Post) {
+	for _, post := range posts {
+		post.sendTo(name)
+	}
 }

From 2f925812201c4ce856584e484af60972e10c91dc Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Sat, 5 Oct 2024 18:34:28 +0500
Subject: [PATCH 07/17] new function added

---
 .gitignore                          |  5 ++++
 exercise3/problem4/problem4.go      | 15 ++++++++++
 exercise3/problem4/problem4_test.go | 45 +++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+)

diff --git a/.gitignore b/.gitignore
index 09944b57..6061dea7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -25,3 +25,8 @@ go.work
 
 # Students
 students.txt
+
+# VS Code
+.vscode/
+*.code-workspace
+.history/
diff --git a/exercise3/problem4/problem4.go b/exercise3/problem4/problem4.go
index 7ca4847f..d3ae48dd 100644
--- a/exercise3/problem4/problem4.go
+++ b/exercise3/problem4/problem4.go
@@ -130,3 +130,18 @@ func (l *LinkedList[T]) findPrevious(value T) (*Element[T], error) {
 	}
 	return current, nil
 }
+
+func (l *LinkedList[T]) Reverse() {
+	var prev, next *Element[T]
+	current := l.head
+	l.tail = current
+
+	for current != nil {
+		next = current.next
+		current.next = prev
+		prev = current
+		current = next
+	}
+
+	l.head = prev
+}
diff --git a/exercise3/problem4/problem4_test.go b/exercise3/problem4/problem4_test.go
index a8c68499..baee2e43 100644
--- a/exercise3/problem4/problem4_test.go
+++ b/exercise3/problem4/problem4_test.go
@@ -451,4 +451,49 @@ func TestLinkedList(t *testing.T) {
 			}
 		})
 	})
+
+	t.Run("Reverse", func(t *testing.T) {
+		table := []struct {
+			list     []any
+			expected []any
+		}{
+			{
+				[]any{1, 2, 3, 4, 5},
+				[]any{5, 4, 3, 2, 1},
+			},
+			{
+				[]any{"a", "b", "c", "d", "e"},
+				[]any{"e", "d", "c", "b", "a"},
+			},
+			{
+				[]any{true, false},
+				[]any{false, true},
+			},
+		}
+
+		for _, r := range table {
+			ll := &LinkedList[any]{}
+			for _, value := range r.list {
+				ll.Add(
+					&Element[any]{
+						value: value,
+					},
+				)
+			}
+
+			ll.Reverse()
+
+			actual := ll.List()
+			if len(actual) != len(r.expected) {
+				t.Errorf("Reverse(%v) was incorrect, got size: %d, expected size: %d", r.list, len(actual), len(r.expected))
+			}
+
+			for i := 0; i < len(actual); i++ {
+				if actual[i] != r.expected[i] {
+					t.Errorf("Reverse(%v) was incorrect, actual value: %v, expect value: %v", r.list, actual[i], r.expected[i])
+				}
+			}
+		}
+
+	})
 }

From 383547f58b55bd8a61bf09fd1b706171efe18b16 Mon Sep 17 00:00:00 2001
From: Aqzhol Baqatay <98736657+aqzholsky@users.noreply.github.com>
Date: Sat, 5 Oct 2024 18:35:37 +0500
Subject: [PATCH 08/17] Delete .vscode/settings.json

---
 .vscode/settings.json | 22 ----------------------
 1 file changed, 22 deletions(-)
 delete mode 100644 .vscode/settings.json

diff --git a/.vscode/settings.json b/.vscode/settings.json
deleted file mode 100644
index 4fe3b603..00000000
--- a/.vscode/settings.json
+++ /dev/null
@@ -1,22 +0,0 @@
-{
-    "workbench.colorCustomizations": {
-        "activityBar.activeBackground": "#fa1b49",
-        "activityBar.background": "#fa1b49",
-        "activityBar.foreground": "#e7e7e7",
-        "activityBar.inactiveForeground": "#e7e7e799",
-        "activityBarBadge.background": "#155e02",
-        "activityBarBadge.foreground": "#e7e7e7",
-        "commandCenter.border": "#e7e7e799",
-        "sash.hoverBorder": "#fa1b49",
-        "statusBar.background": "#dd0531",
-        "statusBar.foreground": "#e7e7e7",
-        "statusBarItem.hoverBackground": "#fa1b49",
-        "statusBarItem.remoteBackground": "#dd0531",
-        "statusBarItem.remoteForeground": "#e7e7e7",
-        "titleBar.activeBackground": "#dd0531",
-        "titleBar.activeForeground": "#e7e7e7",
-        "titleBar.inactiveBackground": "#dd053199",
-        "titleBar.inactiveForeground": "#e7e7e799"
-    },
-    "peacock.color": "#dd0531"
-}
\ No newline at end of file

From 94e0482c1dfdb1b676af84b2f4e9298b2d2ae355 Mon Sep 17 00:00:00 2001
From: Aqzhol Baqatay <98736657+aqzholsky@users.noreply.github.com>
Date: Sat, 5 Oct 2024 18:35:51 +0500
Subject: [PATCH 09/17] Delete .vscode/launch.json

---
 .vscode/launch.json | 15 ---------------
 1 file changed, 15 deletions(-)
 delete mode 100644 .vscode/launch.json

diff --git a/.vscode/launch.json b/.vscode/launch.json
deleted file mode 100644
index 608d3c69..00000000
--- a/.vscode/launch.json
+++ /dev/null
@@ -1,15 +0,0 @@
-{
-    // Use IntelliSense to learn about possible attributes.
-    // Hover to view descriptions of existing attributes.
-    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
-    "version": "0.2.0",
-    "configurations": [
-        {
-            "name": "Launch Package",
-            "type": "go",
-            "request": "launch",
-            "mode": "auto",
-            "program": "${fileDirname}"
-        }
-    ]
-}
\ No newline at end of file

From efa85a13328c7cc79f701d8563204e4a14eb4b9c Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Sat, 5 Oct 2024 18:38:21 +0500
Subject: [PATCH 10/17] description changed

---
 exercise3/problem4/README.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/exercise3/problem4/README.md b/exercise3/problem4/README.md
index dd6ea6bc..35c0b15c 100644
--- a/exercise3/problem4/README.md
+++ b/exercise3/problem4/README.md
@@ -32,4 +32,8 @@ Get the size of the linked list.
 
 Check if the linked list is empty.
 
+- _Reverse_
+
+Reverse linked list by changing the links between elements
+
 ! Please check the tests for signature and more examples.

From 8506459bf6476cdaffea502bbc6153eaedca8a42 Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Tue, 29 Oct 2024 17:31:17 +0500
Subject: [PATCH 11/17] exercise 5 completed

---
 exercise5/problem1/problem1.go |  7 ++++++
 exercise5/problem2/problem2.go | 39 ++++++++++++++++++++++++++++++++++
 exercise5/problem3/problem3.go |  6 +++---
 exercise5/problem4/problem4.go |  1 +
 exercise5/problem5/problem5.go | 21 ++++++++++++++++--
 exercise5/problem6/problem6.go | 31 ++++++++++++++++++++++++---
 exercise5/problem7/problem7.go | 24 ++++++++++++++++++++-
 exercise5/problem8/problem8.go | 14 +++++++++++-
 8 files changed, 133 insertions(+), 10 deletions(-)

diff --git a/exercise5/problem1/problem1.go b/exercise5/problem1/problem1.go
index 4f514fab..8e71df1a 100644
--- a/exercise5/problem1/problem1.go
+++ b/exercise5/problem1/problem1.go
@@ -1,9 +1,16 @@
 package problem1
 
+import "sync"
+
 func incrementConcurrently(num int) int {
+	wg := new(sync.WaitGroup)
+	wg.Add(1)
+
 	go func() {
+		defer wg.Done()
 		num++
 	}()
 
+	wg.Wait()
 	return num
 }
diff --git a/exercise5/problem2/problem2.go b/exercise5/problem2/problem2.go
index 16d38e1d..b568b2fc 100644
--- a/exercise5/problem2/problem2.go
+++ b/exercise5/problem2/problem2.go
@@ -1,5 +1,10 @@
 package problem2
 
+import (
+	"runtime"
+	"sync"
+)
+
 // add - sequential code to add numbers, don't update it, just to illustrate concept
 func add(numbers []int) int64 {
 	var sum int64
@@ -10,7 +15,41 @@ func add(numbers []int) int64 {
 }
 
 func addConcurrently(numbers []int) int64 {
+	cpuCount := runtime.NumCPU()
+	runtime.GOMAXPROCS(cpuCount)
+	chunkSize := len(numbers) / cpuCount
+	resultCh := make(chan int, cpuCount)
+	wg := new(sync.WaitGroup)
+
 	var sum int64
 
+	for i := 0; i < cpuCount; i++ {
+		start := i * chunkSize
+		end := start + chunkSize
+		if i == cpuCount-1 {
+			end = len(numbers)
+		}
+		wg.Add(1)
+		go processAddChunks(numbers[start:end], resultCh, wg)
+	}
+
+	go func() {
+		wg.Wait()
+		close(resultCh)
+	}()
+
+	for result := range resultCh {
+		sum += int64(result)
+	}
+
 	return sum
 }
+
+func processAddChunks(chunk []int, resultCh chan<- int, wg *sync.WaitGroup) {
+	defer wg.Done()
+	result := 0
+	for _, num := range chunk {
+		result += num
+	}
+	resultCh <- result
+}
diff --git a/exercise5/problem3/problem3.go b/exercise5/problem3/problem3.go
index e085a51a..a261335c 100644
--- a/exercise5/problem3/problem3.go
+++ b/exercise5/problem3/problem3.go
@@ -1,11 +1,11 @@
 package problem3
 
 func sum(a, b int) int {
-	var c int
+	ch := make(chan int)
 
 	go func(a, b int) {
-		c = a + b
+		ch <- a + b
 	}(a, b)
 
-	return c
+	return <-ch
 }
diff --git a/exercise5/problem4/problem4.go b/exercise5/problem4/problem4.go
index b5899ddf..f8457faa 100644
--- a/exercise5/problem4/problem4.go
+++ b/exercise5/problem4/problem4.go
@@ -1,6 +1,7 @@
 package problem4
 
 func iter(ch chan<- int, nums []int) {
+	defer close(ch)
 	for _, n := range nums {
 		ch <- n
 	}
diff --git a/exercise5/problem5/problem5.go b/exercise5/problem5/problem5.go
index ac192c58..16c45d89 100644
--- a/exercise5/problem5/problem5.go
+++ b/exercise5/problem5/problem5.go
@@ -1,8 +1,25 @@
 package problem5
 
-func producer() {}
+import "fmt"
 
-func consumer() {}
+func producer(words []string, ch chan<- string) {
+	defer close(ch)
+	for _, word := range words {
+		ch <- word
+	}
+}
+
+func consumer(ch <-chan string) string {
+	var result string
+	for word := range ch {
+		if result == "" {
+			result += word
+		} else {
+			result += fmt.Sprintf(" %s", word)
+		}
+	}
+	return result
+}
 
 func send(
 	words []string,
diff --git a/exercise5/problem6/problem6.go b/exercise5/problem6/problem6.go
index e1beea87..0b0d6691 100644
--- a/exercise5/problem6/problem6.go
+++ b/exercise5/problem6/problem6.go
@@ -2,8 +2,33 @@ package problem6
 
 type pipe func(in <-chan int) <-chan int
 
-var multiplyBy2 pipe = func() {}
+var multiplyBy2 pipe = func(in <-chan int) <-chan int {
+	out := make(chan int)
+	go func() {
+		for v := range in {
+			out <- v * 2
+		}
+		close(out)
+	}()
+	return out
+}
 
-var add5 pipe = func() {}
+var add5 pipe = func(in <-chan int) <-chan int {
+	out := make(chan int)
+	go func() {
+		for v := range in {
+			out <- v + 5
+		}
+		close(out)
+	}()
+	return out
+}
 
-func piper(in <-chan int, pipes []pipe) <-chan int {}
+func piper(in <-chan int, pipes []pipe) <-chan int {
+	var out <-chan int
+	for _, pipe := range pipes {
+		out = pipe(in)
+		in = out
+	}
+	return out
+}
diff --git a/exercise5/problem7/problem7.go b/exercise5/problem7/problem7.go
index c3c1d0c9..267c4842 100644
--- a/exercise5/problem7/problem7.go
+++ b/exercise5/problem7/problem7.go
@@ -1,3 +1,25 @@
 package problem7
 
-func multiplex(ch1 <-chan string, ch2 <-chan string) []string {}
+import "sync"
+
+func multiplex(channels ...<-chan string) []string {
+	result := []string{}
+	wg := new(sync.WaitGroup)
+	wg.Add(len(channels))
+	mx := new(sync.Mutex)
+
+	for _, ch := range channels {
+		go func(c <-chan string) {
+			defer wg.Done()
+			for v := range c {
+				mx.Lock()
+				result = append(result, v)
+				mx.Unlock()
+			}
+		}(ch)
+	}
+
+	wg.Wait()
+
+	return result
+}
diff --git a/exercise5/problem8/problem8.go b/exercise5/problem8/problem8.go
index 3e951b3b..bb2643f0 100644
--- a/exercise5/problem8/problem8.go
+++ b/exercise5/problem8/problem8.go
@@ -4,4 +4,16 @@ import (
 	"time"
 )
 
-func withTimeout(ch <-chan string, ttl time.Duration) string {}
+func withTimeout(ch <-chan string, ttl time.Duration) string {
+	for {
+		select {
+		case msg, ok := <-ch:
+			if !ok {
+				return "channel closed"
+			}
+			return msg
+		case <-time.After(ttl):
+			return "timeout"
+		}
+	}
+}

From 31d0ea3498f34f1fb487d91e5dcb6c1840776c19 Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Wed, 20 Nov 2024 22:35:32 +0500
Subject: [PATCH 12/17] WIP

---
 exercise6/problem1/problem1.go | 19 ++++++++++++++++++-
 exercise6/problem2/problem2.go | 22 ++++++++++++++++++++--
 exercise6/problem3/problem3.go | 14 ++++++++++++++
 3 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/exercise6/problem1/problem1.go b/exercise6/problem1/problem1.go
index ee453b24..ac4d481d 100644
--- a/exercise6/problem1/problem1.go
+++ b/exercise6/problem1/problem1.go
@@ -1,9 +1,26 @@
 package problem1
 
+import "sync"
+
 type bankAccount struct {
 	blnc int
+	mx   *sync.Mutex
 }
 
 func newAccount(blnc int) *bankAccount {
-	return &bankAccount{blnc}
+	return &bankAccount{blnc, &sync.Mutex{}}
+}
+
+func (b *bankAccount) withdraw(amount int) {
+	defer b.mx.Unlock()
+	b.mx.Lock()
+	if b.blnc >= amount {
+		b.blnc -= amount
+	}
+}
+
+func (b *bankAccount) deposit(amount int) {
+	defer b.mx.Unlock()
+	b.mx.Lock()
+	b.blnc += amount
 }
diff --git a/exercise6/problem2/problem2.go b/exercise6/problem2/problem2.go
index 97e02368..037de66e 100644
--- a/exercise6/problem2/problem2.go
+++ b/exercise6/problem2/problem2.go
@@ -1,6 +1,7 @@
 package problem2
 
 import (
+	"sync"
 	"time"
 )
 
@@ -8,13 +9,30 @@ var readDelay = 10 * time.Millisecond
 
 type bankAccount struct {
 	blnc int
+	mx   *sync.RWMutex
 }
 
 func newAccount(blnc int) *bankAccount {
-	return &bankAccount{blnc}
+	return &bankAccount{blnc, &sync.RWMutex{}}
 }
 
 func (b *bankAccount) balance() int {
 	time.Sleep(readDelay)
-	return 0
+	defer b.mx.RUnlock()
+	b.mx.RLock()
+	return b.blnc
+}
+
+func (b *bankAccount) withdraw(amount int) {
+	defer b.mx.Unlock()
+	b.mx.Lock()
+	if b.blnc >= amount {
+		b.blnc -= amount
+	}
+}
+
+func (b *bankAccount) deposit(amount int) {
+	defer b.mx.Unlock()
+	b.mx.Lock()
+	b.blnc += amount
 }
diff --git a/exercise6/problem3/problem3.go b/exercise6/problem3/problem3.go
index b34b90bb..acb946e2 100644
--- a/exercise6/problem3/problem3.go
+++ b/exercise6/problem3/problem3.go
@@ -1,5 +1,7 @@
 package problem3
 
+import "sync/atomic"
+
 type counter struct {
 	val int64
 }
@@ -9,3 +11,15 @@ func newCounter() *counter {
 		val: 0,
 	}
 }
+
+func (c *counter) inc() {
+	atomic.AddInt64(&c.val, 1)
+}
+
+func (c *counter) dec() {
+	atomic.AddInt64(&c.val, -1)
+}
+
+func (c *counter) value() int64 {
+	return atomic.LoadInt64(&c.val)
+}

From 6fa7b661f01b56b6dd51f14fbfa3b748e5eb9434 Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Tue, 3 Dec 2024 21:38:18 +0500
Subject: [PATCH 13/17] exercise 6 completed

---
 exercise6/problem4/problem4.go | 23 ++++++++++++++++++-----
 exercise6/problem5/problem5.go | 21 ++++++++++++++++-----
 exercise6/problem6/problem6.go |  5 ++---
 exercise6/problem7/problem7.go | 12 +++++++++++-
 exercise6/problem8/problem8.go | 24 +++++++++++++++++++++++-
 5 files changed, 70 insertions(+), 15 deletions(-)

diff --git a/exercise6/problem4/problem4.go b/exercise6/problem4/problem4.go
index 793449c9..7f53e5ef 100644
--- a/exercise6/problem4/problem4.go
+++ b/exercise6/problem4/problem4.go
@@ -1,31 +1,44 @@
 package problem4
 
 import (
+	"sync"
 	"time"
 )
 
-func worker(id int, _ *[]string, ch chan<- int) {
-	// TODO wait for shopping list to be completed
+func worker(id int, shoppingList *[]string, ch chan<- int, cond *sync.Cond) {
+	defer cond.L.Unlock()
+	cond.L.Lock()
+
+	if len(*shoppingList) == 0 {
+		cond.Wait()
+	}
+
 	ch <- id
 }
 
-func updateShopList(shoppingList *[]string) {
+func updateShopList(shoppingList *[]string, cond *sync.Cond) {
 	time.Sleep(10 * time.Millisecond)
 
+	defer cond.L.Unlock()
+	cond.L.Lock()
+
 	*shoppingList = append(*shoppingList, "apples")
 	*shoppingList = append(*shoppingList, "milk")
 	*shoppingList = append(*shoppingList, "bake soda")
+
+	cond.Signal()
 }
 
 func notifyOnShopListUpdate(shoppingList *[]string, numWorkers int) <-chan int {
 	notifier := make(chan int)
+	cond := &sync.Cond{L: &sync.Mutex{}}
 
 	for i := range numWorkers {
-		go worker(i+1, shoppingList, notifier)
+		go worker(i+1, shoppingList, notifier, cond)
 		time.Sleep(time.Millisecond) // order matters
 	}
 
-	go updateShopList(shoppingList)
+	go updateShopList(shoppingList, cond)
 
 	return notifier
 }
diff --git a/exercise6/problem5/problem5.go b/exercise6/problem5/problem5.go
index 8e4a1703..a54d8522 100644
--- a/exercise6/problem5/problem5.go
+++ b/exercise6/problem5/problem5.go
@@ -1,31 +1,42 @@
 package problem5
 
 import (
+	"sync"
 	"time"
 )
 
-func worker(id int, shoppingList *[]string, ch chan<- int) {
-	// TODO wait for shopping list to be completed
+func worker(id int, shoppingList *[]string, ch chan<- int, cond *sync.Cond) {
+	defer cond.L.Unlock()
+	cond.L.Lock()
+	for len(*shoppingList) == 0 {
+		cond.Wait()
+	}
 	ch <- id
 }
 
-func updateShopList(shoppingList *[]string) {
+func updateShopList(shoppingList *[]string, cond *sync.Cond) {
 	time.Sleep(10 * time.Millisecond)
 
+	defer cond.L.Unlock()
+	cond.L.Lock()
+
 	*shoppingList = append(*shoppingList, "apples")
 	*shoppingList = append(*shoppingList, "milk")
 	*shoppingList = append(*shoppingList, "bake soda")
+
+	cond.Broadcast()
 }
 
 func notifyOnShopListUpdate(shoppingList *[]string, numWorkers int) <-chan int {
 	notifier := make(chan int)
+	cond := &sync.Cond{L: &sync.Mutex{}}
 
 	for i := range numWorkers {
-		go worker(i+1, shoppingList, notifier)
+		go worker(i+1, shoppingList, notifier, cond)
 		time.Sleep(time.Millisecond) // order matters
 	}
 
-	go updateShopList(shoppingList)
+	go updateShopList(shoppingList, cond)
 
 	return notifier
 }
diff --git a/exercise6/problem6/problem6.go b/exercise6/problem6/problem6.go
index 0c1122b9..fcbf38a7 100644
--- a/exercise6/problem6/problem6.go
+++ b/exercise6/problem6/problem6.go
@@ -6,14 +6,13 @@ import (
 
 func runTasks(init func()) {
 	var wg sync.WaitGroup
+	onceInit := sync.OnceFunc(init)
 
 	for range 10 {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
-
-			//TODO: modify so that load function gets called only once.
-			init()
+			onceInit()
 		}()
 	}
 	wg.Wait()
diff --git a/exercise6/problem7/problem7.go b/exercise6/problem7/problem7.go
index ef49497b..d54925e3 100644
--- a/exercise6/problem7/problem7.go
+++ b/exercise6/problem7/problem7.go
@@ -3,17 +3,27 @@ package problem7
 import (
 	"fmt"
 	"math/rand"
+	"sync"
 	"time"
 )
 
 func task() {
 	start := time.Now()
 	var t *time.Timer
+	mx := &sync.Mutex{}
+
 	t = time.AfterFunc(
 		randomDuration(),
 		func() {
+			defer mx.Unlock()
+			mx.Lock()
 			fmt.Println(time.Now().Sub(start))
-			t.Reset(randomDuration())
+
+			func() {
+				defer mx.Unlock()
+				mx.Lock()
+				t.Reset(randomDuration())
+			}()
 		},
 	)
 	time.Sleep(5 * time.Second)
diff --git a/exercise6/problem8/problem8.go b/exercise6/problem8/problem8.go
index 949eb2d2..db71fcf9 100644
--- a/exercise6/problem8/problem8.go
+++ b/exercise6/problem8/problem8.go
@@ -1,3 +1,25 @@
 package problem8
 
-func multiplex(chs []<-chan string) []string {}
+import "sync"
+
+func multiplex(chs []<-chan string) []string {
+	result := []string{}
+	wg := new(sync.WaitGroup)
+	wg.Add(len(chs))
+	mx := new(sync.Mutex)
+
+	for _, ch := range chs {
+		go func(c <-chan string) {
+			defer wg.Done()
+			for v := range c {
+				mx.Lock()
+				result = append(result, v)
+				mx.Unlock()
+			}
+		}(ch)
+	}
+
+	wg.Wait()
+
+	return result
+}

From 3792fb5172eb1cfd801e325234679580d57b5723 Mon Sep 17 00:00:00 2001
From: aqzholsky <98736657+aqzholsky@users.noreply.github.com>
Date: Tue, 3 Dec 2024 21:43:47 +0500
Subject: [PATCH 14/17] exercise 6 problem 8 solution changed

---
 exercise6/problem8/problem8.go | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/exercise6/problem8/problem8.go b/exercise6/problem8/problem8.go
index db71fcf9..6c6ef8b7 100644
--- a/exercise6/problem8/problem8.go
+++ b/exercise6/problem8/problem8.go
@@ -5,21 +5,26 @@ import "sync"
 func multiplex(chs []<-chan string) []string {
 	result := []string{}
 	wg := new(sync.WaitGroup)
-	wg.Add(len(chs))
-	mx := new(sync.Mutex)
+	resultCh := make(chan string)
 
 	for _, ch := range chs {
+		wg.Add(1)
 		go func(c <-chan string) {
 			defer wg.Done()
 			for v := range c {
-				mx.Lock()
-				result = append(result, v)
-				mx.Unlock()
+				resultCh <- v
 			}
 		}(ch)
 	}
 
-	wg.Wait()
+	go func() {
+		wg.Wait()
+		close(resultCh)
+	}()
+
+	for v := range resultCh {
+		result = append(result, v)
+	}
 
 	return result
 }

From 9f9105bc0635910c5c19aaa8e48d88490b0bf7a7 Mon Sep 17 00:00:00 2001
From: Talgat <talgat.s@protonmail.com>
Date: Tue, 26 Nov 2024 18:22:45 +0500
Subject: [PATCH 15/17] add lesson7

---
 exercise7/blogging-platform/README.md         |  3 +
 exercise7/blogging-platform/go.mod            |  5 ++
 exercise7/blogging-platform/go.sum            |  2 +
 exercise7/blogging-platform/main.go           | 49 ++++++++++++
 .../pkg/httputils/request/body.go             | 76 +++++++++++++++++++
 .../pkg/httputils/response/body.go            | 33 ++++++++
 .../pkg/httputils/statusError/main.go         | 18 +++++
 7 files changed, 186 insertions(+)
 create mode 100644 exercise7/blogging-platform/README.md
 create mode 100644 exercise7/blogging-platform/go.mod
 create mode 100644 exercise7/blogging-platform/go.sum
 create mode 100644 exercise7/blogging-platform/main.go
 create mode 100644 exercise7/blogging-platform/pkg/httputils/request/body.go
 create mode 100644 exercise7/blogging-platform/pkg/httputils/response/body.go
 create mode 100644 exercise7/blogging-platform/pkg/httputils/statusError/main.go

diff --git a/exercise7/blogging-platform/README.md b/exercise7/blogging-platform/README.md
new file mode 100644
index 00000000..e6ef7017
--- /dev/null
+++ b/exercise7/blogging-platform/README.md
@@ -0,0 +1,3 @@
+# Blogging Platform
+
+Please check https://roadmap.sh/projects/blogging-platform-api.
diff --git a/exercise7/blogging-platform/go.mod b/exercise7/blogging-platform/go.mod
new file mode 100644
index 00000000..ca16e703
--- /dev/null
+++ b/exercise7/blogging-platform/go.mod
@@ -0,0 +1,5 @@
+module github.com/talgat-ruby/exercises-go/exercise7/blogging-platform
+
+go 1.23.3
+
+require github.com/lib/pq v1.10.9
diff --git a/exercise7/blogging-platform/go.sum b/exercise7/blogging-platform/go.sum
new file mode 100644
index 00000000..aeddeae3
--- /dev/null
+++ b/exercise7/blogging-platform/go.sum
@@ -0,0 +1,2 @@
+github.com/lib/pq v1.10.9 h1:YXG7RB+JIjhP29X+OtkiDnYaXQwpS4JEWq7dtCCRUEw=
+github.com/lib/pq v1.10.9/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
diff --git a/exercise7/blogging-platform/main.go b/exercise7/blogging-platform/main.go
new file mode 100644
index 00000000..1ffa1477
--- /dev/null
+++ b/exercise7/blogging-platform/main.go
@@ -0,0 +1,49 @@
+package main
+
+import (
+	"context"
+	"log/slog"
+	"os"
+	"os/signal"
+
+	"github.com/talgat-ruby/exercises-go/exercise7/blogging-platform/internal/api"
+	"github.com/talgat-ruby/exercises-go/exercise7/blogging-platform/internal/db"
+)
+
+func main() {
+	ctx, cancel := context.WithCancel(context.Background())
+
+	// db
+	_, err := db.New()
+	if err != nil {
+		slog.ErrorContext(
+			ctx,
+			"initialize service error",
+			"service", "db",
+			"error", err,
+		)
+		panic(err)
+	}
+
+	// api
+	a := api.New()
+	if err := a.Start(ctx); err != nil {
+		slog.ErrorContext(
+			ctx,
+			"initialize service error",
+			"service", "api",
+			"error", err,
+		)
+		panic(err)
+	}
+
+	go func() {
+		shutdown := make(chan os.Signal, 1)   // Create channel to signify s signal being sent
+		signal.Notify(shutdown, os.Interrupt) // When an interrupt is sent, notify the channel
+
+		sig := <-shutdown
+		slog.WarnContext(ctx, "signal received - shutting down...", "signal", sig)
+
+		cancel()
+	}()
+}
diff --git a/exercise7/blogging-platform/pkg/httputils/request/body.go b/exercise7/blogging-platform/pkg/httputils/request/body.go
new file mode 100644
index 00000000..92d639f4
--- /dev/null
+++ b/exercise7/blogging-platform/pkg/httputils/request/body.go
@@ -0,0 +1,76 @@
+package request
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+
+	"github.com/talgat-ruby/exercises-go/exercise7/blogging-platform/pkg/httputils/statusError"
+)
+
+func JSON(w http.ResponseWriter, r *http.Request, dst interface{}) error {
+	ct := r.Header.Get("Content-Type")
+	if ct != "" {
+		mediaType := strings.ToLower(strings.TrimSpace(strings.Split(ct, ";")[0]))
+		if mediaType != "application/json" {
+			msg := "Content-Type header is not application/json"
+			return statusError.New(http.StatusUnsupportedMediaType, msg)
+		}
+	}
+
+	r.Body = http.MaxBytesReader(w, r.Body, 1048576)
+
+	dec := json.NewDecoder(r.Body)
+	dec.DisallowUnknownFields()
+
+	err := dec.Decode(&dst)
+	if err != nil {
+		var syntaxError *json.SyntaxError
+		var unmarshalTypeError *json.UnmarshalTypeError
+
+		switch {
+		case errors.As(err, &syntaxError):
+			msg := fmt.Sprintf("Request body contains badly-formed JSON (at position %d)", syntaxError.Offset)
+			return statusError.New(http.StatusBadRequest, msg)
+
+		case errors.Is(err, io.ErrUnexpectedEOF):
+			msg := "Request body contains badly-formed JSON"
+			return statusError.New(http.StatusBadRequest, msg)
+
+		case errors.As(err, &unmarshalTypeError):
+			msg := fmt.Sprintf(
+				"Request body contains an invalid value for the %q field (at position %d)",
+				unmarshalTypeError.Field,
+				unmarshalTypeError.Offset,
+			)
+			return statusError.New(http.StatusBadRequest, msg)
+
+		case strings.HasPrefix(err.Error(), "json: unknown field "):
+			fieldName := strings.TrimPrefix(err.Error(), "json: unknown field ")
+			msg := fmt.Sprintf("Request body contains unknown field %s", fieldName)
+			return statusError.New(http.StatusBadRequest, msg)
+
+		case errors.Is(err, io.EOF):
+			msg := "Request body must not be empty"
+			return statusError.New(http.StatusBadRequest, msg)
+
+		case err.Error() == "http: request body too large":
+			msg := "Request body must not be larger than 1MB"
+			return statusError.New(http.StatusRequestEntityTooLarge, msg)
+
+		default:
+			return err
+		}
+	}
+
+	err = dec.Decode(&struct{}{})
+	if !errors.Is(err, io.EOF) {
+		msg := "Request body must only contain a single JSON object"
+		return statusError.New(http.StatusBadRequest, msg)
+	}
+
+	return nil
+}
diff --git a/exercise7/blogging-platform/pkg/httputils/response/body.go b/exercise7/blogging-platform/pkg/httputils/response/body.go
new file mode 100644
index 00000000..e1fd78a8
--- /dev/null
+++ b/exercise7/blogging-platform/pkg/httputils/response/body.go
@@ -0,0 +1,33 @@
+package response
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+)
+
+type DataResponse struct {
+	Data interface{} `json:"data"`
+}
+
+func JSON(w http.ResponseWriter, status int, data interface{}) error {
+	if data == nil {
+		w.WriteHeader(http.StatusNoContent)
+		return nil
+	}
+
+	js, err := json.Marshal(data)
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return fmt.Errorf("JSON marshal error: %w", err)
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	if _, err := w.Write(js); err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return fmt.Errorf("writer error: %w", err)
+	}
+
+	return nil
+}
diff --git a/exercise7/blogging-platform/pkg/httputils/statusError/main.go b/exercise7/blogging-platform/pkg/httputils/statusError/main.go
new file mode 100644
index 00000000..6cf4e1b6
--- /dev/null
+++ b/exercise7/blogging-platform/pkg/httputils/statusError/main.go
@@ -0,0 +1,18 @@
+package statusError
+
+type StatusError struct {
+	status int
+	msg    string
+}
+
+func New(status int, msg string) error {
+	return &StatusError{status, msg}
+}
+
+func (st *StatusError) Error() string {
+	return st.msg
+}
+
+func (st *StatusError) Status() int {
+	return st.status
+}

From 48a4b158120966defe92a4a31ccf1351789f8793 Mon Sep 17 00:00:00 2001
From: Talgat <talgat.s@pm.me>
Date: Thu, 23 Jan 2025 19:03:48 +0500
Subject: [PATCH 16/17] add exercise9

---
 exercise9/README.md | 42 ++++++++++++++++++++++++++++++++++++++++++
 exercise9/go.mod    |  3 +++
 2 files changed, 45 insertions(+)
 create mode 100644 exercise9/README.md
 create mode 100644 exercise9/go.mod

diff --git a/exercise9/README.md b/exercise9/README.md
new file mode 100644
index 00000000..5d54880e
--- /dev/null
+++ b/exercise9/README.md
@@ -0,0 +1,42 @@
+# Exercise 9
+
+Project <https://roadmap.sh/projects/fitness-workout-tracker>
+
+## Teams
+
+Team 1
+
+1. Имангали Аскар (controller)
+2. Зернов Владислав (controller)
+3. Курмашев Сабит (api)
+4. Кабулов Нуртас (api)
+5. Омаров Темирлан (db)
+6. Сагиндиков Меирбек (db)
+
+Team 2
+
+1. Тұрарова Айзада (controller)
+2. Толеу Аян (controller)
+3. Мырзаханов Алинур (api)
+4. Еркибаев Зураб (api)
+5. Бақатай Ақжол (db)
+6. Бимаканова Мадина (db)
+
+Team 3
+
+1. Кабдылкак Арнур (controller)
+2. Калкин Ернар (controller)
+3. Манкенов Арай (api)
+4. Усербай Асылбек (api)
+5. Камбаров Руслан (db)
+6. Қайратұлы Шыңғысхан (db)
+
+Team 4
+
+1. Жақуда Жарқынай (controller)
+2. Жантасов Адлет (controller)
+3. Туралин Аргын (api)
+4. Алтынбек Жандос (api)
+5. Жакупов Жандаулет (db)
+6. Мұхаметқали Арайлым (db)
+7. Кемалатдин Ғалымжан (your choice)
diff --git a/exercise9/go.mod b/exercise9/go.mod
new file mode 100644
index 00000000..72f28b6f
--- /dev/null
+++ b/exercise9/go.mod
@@ -0,0 +1,3 @@
+module github.com/talgat-ruby/exercises-go/exercise9
+
+go 1.23.5

From 2ecb6e20a278605f638cfe49dd9ee66e08bddda9 Mon Sep 17 00:00:00 2001
From: Talgat <talgat.s@pm.me>
Date: Mon, 27 Jan 2025 18:18:10 +0500
Subject: [PATCH 17/17] update exercise9

---
 exercise9/README.md | 40 ++++++----------------------------------
 1 file changed, 6 insertions(+), 34 deletions(-)

diff --git a/exercise9/README.md b/exercise9/README.md
index 5d54880e..ef1d468e 100644
--- a/exercise9/README.md
+++ b/exercise9/README.md
@@ -6,37 +6,9 @@ Project <https://roadmap.sh/projects/fitness-workout-tracker>
 
 Team 1
 
-1. Имангали Аскар (controller)
-2. Зернов Владислав (controller)
-3. Курмашев Сабит (api)
-4. Кабулов Нуртас (api)
-5. Омаров Темирлан (db)
-6. Сагиндиков Меирбек (db)
-
-Team 2
-
-1. Тұрарова Айзада (controller)
-2. Толеу Аян (controller)
-3. Мырзаханов Алинур (api)
-4. Еркибаев Зураб (api)
-5. Бақатай Ақжол (db)
-6. Бимаканова Мадина (db)
-
-Team 3
-
-1. Кабдылкак Арнур (controller)
-2. Калкин Ернар (controller)
-3. Манкенов Арай (api)
-4. Усербай Асылбек (api)
-5. Камбаров Руслан (db)
-6. Қайратұлы Шыңғысхан (db)
-
-Team 4
-
-1. Жақуда Жарқынай (controller)
-2. Жантасов Адлет (controller)
-3. Туралин Аргын (api)
-4. Алтынбек Жандос (api)
-5. Жакупов Жандаулет (db)
-6. Мұхаметқали Арайлым (db)
-7. Кемалатдин Ғалымжан (your choice)
+1. Тұрарова Айзада (api)
+2. Манкенов Арай (api)
+3. Усербай Асылбек (controller)
+4. Кемалатдин Ғалымжан (controller)
+5. Имангали Аскар (db)
+6. Кабдылкак Арнур (db)