Add LSA of BST solution in TS

Author: Jeehay28

lowest-common-ancestor-of-a-binary-search-tree/Jeehay28.ts

@@ -0,0 +1,53 @@
+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;
+  }
+}
+
+// TC: O(n)
+// SC: O(1)
+function lowestCommonAncestor(
+  root: TreeNode | null,
+  p: TreeNode | null,
+  q: TreeNode | null
+): TreeNode | null {
+  if (!root || !p || !q) return null;
+
+  let node = root;
+
+  while (node) {
+    if (node.val < p.val && node.val < q.val) {
+      node = node.right!;
+    } else if (node.val > p.val && node.val > q.val) {
+      node = node.left!;
+    } else {
+      return node;
+    }
+  }
+
+  return null;
+}
+
+
+// TC: O(n)
+// SC: O(n)
+// function lowestCommonAncestor(
+//   root: TreeNode | null,
+//   p: TreeNode | null,
+//   q: TreeNode | null
+// ): TreeNode | null {
+//   if (!root || !p || !q) return null;
+
+//   if (p.val < root.val && q.val < root.val) {
+//     return lowestCommonAncestor(root.left, p, q);
+//   } else if (p.val > root.val && q.val > root.val) {
+//     return lowestCommonAncestor(root.right, p, q);
+//   } else {
+//     return root;
+//   }
+// }