solve: kth smallest element in a bst

Author: tolluset

kth-smallest-element-in-a-bst/tolluset.ts

@@ -0,0 +1,42 @@
+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(n)
+ * */
+function kthSmallest(root: TreeNode, k: number): number {
+  let count = 0;
+  let result: null | number = null;
+
+  const inOrder = (node: TreeNode | null) => {
+    if (!node || result !== null) {
+      return false;
+    }
+
+    if (inOrder(node.left)) {
+      return true;
+    }
+
+    count++;
+
+    if (count === k) {
+      result = node.val;
+      return true;
+    }
+
+    inOrder(node.right);
+  };
+
+  inOrder(root);
+
+  return result!;
+}