add Lowest Common Ancestor of a Binary Search Tree solution

Author: HoonDongKang

lowest-common-ancestor-of-a-binary-search-tree/HoonDongKang.ts

@@ -0,0 +1,63 @@
+/**
+ * [Problem]: [235] Lowest Common Ancestor of a Binary Search Tree
+ * (https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description/)
+ */
+
+class TreeNode {
+    val: number;
+    left: TreeNode | null;
+    right: TreeNode | null;
+    constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+        this.val = val === undefined ? 0 : val;
+        this.left = left === undefined ? null : left;
+        this.right = right === undefined ? null : right;
+    }
+}
+
+function lowestCommonAncestor(
+    root: TreeNode | null,
+    p: TreeNode | null,
+    q: TreeNode | null
+): TreeNode | null {
+    //시간복잡도 O(h)
+    //공간복잡도 O(h)
+    function recursiveFunc(
+        root: TreeNode | null,
+        p: TreeNode | null,
+        q: TreeNode | null
+    ): TreeNode | null {
+        if (!p || !root || !q) return null;
+        if (p.val < root.val && q.val < root.val) {
+            return recursiveFunc(root.left, p, q);
+        }
+        if (root.val < p.val && root.val < q.val) {
+            return recursiveFunc(root.right, p, q);
+        }
+
+        return root;
+    }
+
+    //시간복잡도 O(h)
+    //공간복잡도 O(1)
+    function loopFunc(
+        root: TreeNode | null,
+        p: TreeNode | null,
+        q: TreeNode | null
+    ): TreeNode | null {
+        if (!p || !q || !root) return null;
+
+        let node = root;
+
+        while (node) {
+            if (p.val < node.val && q.val < node.val) {
+                node = node?.left!;
+            } else if (p.val > node.val && q.val > node.val) {
+                node = node?.right!;
+            } else {
+                return node;
+            }
+        }
+
+        return null;
+    }
+}