feat(datastructures, puzzles): find the closest value in a binary search tree

DIRECTORY.md

@@ -545,6 +545,8 @@
         * [Test Cyclically Shifted Array](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/search/binary_search/cyclically_shifted_array/test_cyclically_shifted_array.py)
       * Find Closest Number
         * [Test Find Closest Number](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/search/binary_search/find_closest_number/test_find_closest_number.py)
+      * Find Closest Value
+        * [Test Find Closest Value](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/search/binary_search/find_closest_value/test_find_closest_value.py)
       * Find First In Duplicate List
         * [Test Find First In Duplicates](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/search/binary_search/find_first_in_duplicate_list/test_find_first_in_duplicates.py)
       * Find Fixed Number

datastructures/trees/binary/search_tree/__init__.py

@@ -219,6 +219,52 @@ def find_second_largest(self) -> BinaryTreeNode:
 
         return current
 
+    def find_closest_value_in_bst(self, target: T) -> Optional[BinaryTreeNode]:
+        """
+        Finds the closest value in the binary search tree to the given target value.
+
+        Args:
+            target T: Value to search for
+        Returns:
+            Node with the closest value to the target
+        """
+        # edge case for empty nodes, if none is provided, we can't find a value that is close to the target
+        if not self.root:
+            return None
+
+        # if the node's data is the target, exit early by returning it
+        if self.root.data == target:
+            return self.root
+
+        # this keeps track of the minimum on both the left and the right
+        min_diff = min_diff_left = min_diff_right = float("inf")
+        closest_value = None
+        fifo_queue = FifoQueue()
+        fifo_queue.enqueue(self.root)
+
+        # while the queue is not empty, we pop off nodes from the queue and check for their values
+        while not fifo_queue.is_empty():
+            current_node = fifo_queue.dequeue()
+
+            min_diff_left = abs(target - current_node.data)
+            min_diff_right = abs(target - current_node.data)
+
+            if min_diff_left < min_diff:
+                min_diff = min_diff_left
+                closest_value = current_node
+
+            if min_diff_right < min_diff:
+                min_diff = min_diff_right
+                closest_value = current_node
+
+            if current_node.left:
+                fifo_queue.enqueue(current_node.left)
+
+            if current_node.right:
+                fifo_queue.enqueue(current_node.right)
+
+        return closest_value
+
     def range_sum(self, low: int, high: int):
         """
         returns the sum of datas of all nodes with a data in the range [low, high].

puzzles/search/binary_search/find_closest_number/README.md

@@ -1,8 +1,7 @@
 # Find the Closest Number
 
-we will be given a sorted array and a target number. Our goal is to find a number in the array that is closest to the
-target number. We will be making use of a binary search to solve this problem, so make sure that you have gone through
-the previous lesson.
+We will be given a sorted array and a target number. Our goal is to find a number in the array that is closest to the
+target number. We will be making use of a binary search to solve this problem.
 
 The array may contain duplicate values and negative numbers.
 

puzzles/search/binary_search/find_closest_value/README.md

@@ -0,0 +1,43 @@
+# Find Closest Value in BST
+
+Write a function that takes in a Binary Search Tree (BST) and a target integer
+value and returns the closest value to that target value contained in the BST.
+
+You can assume that there will only be one closest value.
+
+Each <span>BST</span> node has an integer <span>value</span>, a
+<span>left</span> child node, and a <span>right</span> child node. A node is
+said to be a valid <span>BST</span> node if and only if it satisfies the BST
+property: its <span>value</span> is strictly greater than the values of every
+node to its left; its <span>value</span> is less than or equal to the values
+of every node to its right; and its children nodes are either valid
+<span>BST</span> nodes themselves or <span>None</span> / <span>null</span>.
+
+Sample Input:
+
+```text
+tree =   10
+       /     \
+      5      15
+    /   \   /   \
+   2     5 13   22
+ /           \
+1            14
+target = 12
+```
+
+Sample output: 13
+
+## Hints
+
+- Try traversing the BST node by node, all the while keeping track of the node with the value closest to the target value. 
+  Calculating the absolute value of the difference between a node's value and the target value should allow you to 
+  check if that node is closer than the current closest one.
+- Make use of the BST property to determine what side of any given node has values close to the target value and is 
+  therefore worth exploring.
+- What are the advantages and disadvantages of solving this problem iteratively as opposed to recursively?
+
+## Optimal Space & Time Complexity
+
+Average: O(log(n)) time | O(1) space where n is the number of nodes in the tree
+BST Worst: O(n) time | O(1) space where n is the number of nodes in the tree

puzzles/search/binary_search/find_closest_value/__init__.py

@@ -0,0 +1,42 @@
+from typing import Optional
+from queue import Queue
+from datastructures.trees.binary.search_tree import BinaryTreeNode
+
+
+def find_closest_value_in_bst(node: BinaryTreeNode, target: int) -> Optional[int]:
+    # edge case for empty nodes, if none is provided, we can't find a value that is close to the target
+    if not node:
+        return None
+
+    # if the node's data is the target, exit early by returning it
+    if node.data == target:
+        return node.data
+
+    # this keeps track of the minimum on both the left and the right
+    min_diff = min_diff_left = min_diff_right = float("inf")
+    closest_value = None
+    fifo_queue = Queue()
+    fifo_queue.put(node)
+
+    # while the queue is not empty, we pop off nodes from the queue and check for their values
+    while not fifo_queue.empty():
+        current_node = fifo_queue.get()
+
+        min_diff_left = abs(target - current_node.data)
+        min_diff_right = abs(target - current_node.data)
+
+        if min_diff_left < min_diff:
+            min_diff = min_diff_left
+            closest_value = current_node.data
+
+        if min_diff_right < min_diff:
+            min_diff = min_diff_right
+            closest_value = current_node.data
+
+        if current_node.left:
+            fifo_queue.put(current_node.left)
+
+        if current_node.right:
+            fifo_queue.put(current_node.right)
+
+    return closest_value

puzzles/search/binary_search/find_closest_value/test_find_closest_value.py

@@ -0,0 +1,31 @@
+import unittest
+from datastructures.trees.binary.search_tree import BinaryTreeNode
+from . import find_closest_value_in_bst
+
+
+class FindClosestValueTestCases(unittest.TestCase):
+    def test_something(self):
+        root = BinaryTreeNode(
+            data=10,
+            left=BinaryTreeNode(data=5,
+                                left=BinaryTreeNode(
+                                    data=2,
+                                    left=BinaryTreeNode(data=1),
+                                    right=BinaryTreeNode(data=5))
+                                ),
+            right=BinaryTreeNode(data=15,
+                                 left=BinaryTreeNode(
+                                     data=13,
+                                     right=BinaryTreeNode(
+                                         data=14,
+                                         right=BinaryTreeNode(data=22)
+                                     )
+                                 ))
+        )
+        expected = 13
+        actual = find_closest_value_in_bst(root, target=12)
+        self.assertEqual(expected, actual)
+
+
+if __name__ == '__main__':
+    unittest.main()