Feat: 235. Lowest Common Ancestor of a Binary Search Tree

Author: HC-kang

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

@@ -0,0 +1,52 @@
+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;
+  }
+}
+
+/**
+ * https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description
+ * T.C. O(log n)
+ * S.C. O(log n)
+ */
+function lowestCommonAncestor(
+  root: TreeNode | null,
+  p: TreeNode | null,
+  q: TreeNode | null
+): TreeNode | null {
+  if (!root) return null;
+  if (root.val > p!.val && root.val > q!.val) {
+    return lowestCommonAncestor(root.left, p, q);
+  } else if (root.val < p!.val && root.val < q!.val) {
+    return lowestCommonAncestor(root.right, p, q);
+  } else {
+    return root;
+  }
+}
+
+/**
+ * iterative
+ * T.C. O(log n)
+ * S.C. O(1)
+ */
+function lowestCommonAncestor(
+  root: TreeNode | null,
+  p: TreeNode | null,
+  q: TreeNode | null
+): TreeNode | null {
+  while (root) {
+    if (root.val > p!.val && root.val > q!.val) {
+      root = root.left;
+    } else if (root.val < p!.val && root.val < q!.val) {
+      root = root.right;
+    } else {
+      return root;
+    }
+  }
+  return null;
+}