solve: kth smallest element in a bst

Author: wogha95

kth-smallest-element-in-a-bst/wogha95.js

@@ -0,0 +1,41 @@
+// TC: O(N)
+// SC: O(N)
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @param {number} k
+ * @return {number}
+ */
+var kthSmallest = function (root, k) {
+  let result = null;
+
+  dfs(root);
+
+  return result;
+
+  function dfs(current) {
+    if (result !== null) {
+      return;
+    }
+    if (!current) {
+      return;
+    }
+
+    dfs(current.left);
+    if (current.val >= 0) {
+      if (k === 1) {
+        result = current.val;
+      }
+      k -= 1;
+    }
+    dfs(current.right);
+  }
+};