kth smallest element in a bst solution

Author: hyer0705

kth-smallest-element-in-a-bst/hyer0705.ts

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+/**
+ * Definition for a binary tree node.
+ * 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)
+ *     }
+ * }
+ */
+
+// Time Complexity: O(k) - 최악의 경우 모든 노드를 방문하면 O(n)
+// Space Complexity: O(h) - 재귀 호출 스택의 최대 깊이 (h는 트리의 높이)
+function kthSmallest(root: TreeNode | null, k: number): number {
+  let count = 0;
+  let result = 0;
+
+  const inorder = (node: TreeNode | null): void => {
+    if (!node) return;
+
+    inorder(node.left);
+
+    count++;
+    if (count === k) {
+      result = node.val;
+      return;
+    }
+
+    inorder(node.right);
+  };
+
+  inorder(root);
+
+  return result;
+}