added go implementation

Go/shorturl.go

@@ -0,0 +1,44 @@
+//ShortURL: Bijective conversion between natural numbers (IDs) and short strings
+//Licensed under the MIT License (https://opensource.org/licenses/MIT)
+//
+//shorturl.Encode() takes an ID and turns it into a short string
+//shorturl.Decode() takes a short string and turns it into an ID
+//
+// Example output:
+// 123456789 <=> pgK8p
+
+package shorturl
+
+import "strings"
+
+const (
+	alphabet    = "23456789bcdfghjkmnpqrstvwxyzBCDFGHJKLMNPQRSTVWXYZ-_"
+	alphabetLen = len(alphabet)
+)
+
+func Encode(n int) string {
+	sb := strings.Builder{}
+	for n > 0 {
+		sb.WriteByte(alphabet[n%alphabetLen])
+		n = n / alphabetLen
+	}
+
+	return reverse(sb.String())
+}
+
+func Decode(s string) (n int) {
+	for _, r := range s {
+		n = n*alphabetLen + strings.IndexRune(alphabet, r)
+	}
+	return
+}
+
+func reverse(s string) string {
+	runes := []rune(s)
+	lastIndex := len(s) - 1
+
+	for i := 0; i < len(runes)/2; i++ {
+		runes[i], runes[lastIndex-i] = runes[lastIndex-i], runes[i]
+	}
+	return string(runes)
+}

Go/shorturl_test.go

@@ -0,0 +1,31 @@
+package shorturl
+
+import "testing"
+
+func TestEncode(t *testing.T) {
+	expected := "pgK8p"
+	received := Encode(123456789)
+	if received != expected {
+		t.Fatalf("Expected: %s, received: %s", expected, received)
+	}
+}
+
+func TestDecode(t *testing.T) {
+	expected := 123456789
+	received := Decode("pgK8p")
+	if received != expected {
+		t.Fatalf("Expected: %d, received: %d", expected, received)
+	}
+}
+
+func BenchmarkEncode(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		Encode(n)
+	}
+}
+
+func BenchmarkDecode(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		Decode("BCDFGHJP")
+	}
+}