/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */ class Solution { int res = 0; int rank = 0; public int kthSmallest(TreeNode root, int k) { traverse(root,k); return res; } void traverse(TreeNode root,int k){ if(root == null){ return ; } traverse(root.left,k); rank++; if(k == rank){ res = root.val; return; } traverse(root.right,k); } }