230. Kth Smallest Element in a BST

Aug 13

Author: TonyKim9401

kth-smallest-element-in-a-bst/TonyKim9401.java

@@ -0,0 +1,18 @@
+class Solution {
+    private List<Integer> nums = new ArrayList<>();
+    public int kthSmallest(TreeNode root, int k) {
+        visitTreeNode(root);
+        return nums.get(k-1);
+    }
+
+    public void visitTreeNode(TreeNode node) {
+        if (node == null) return;
+
+        // left < right
+        visitTreeNode(node.left);
+        nums.add(node.val);
+        visitTreeNode(node.right);
+    }
+    // time complexity: O(n), visit all nodes once
+    // space complexity: O(1), used an array list
+}