二叉搜索树的第k个节点

/*
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;

public TreeNode(int val) {
this.val = val;

}

}
*/
public class Solution {
private int num = 0 ;
TreeNode KthNode(TreeNode pRoot, int k){
if(k == 0)return null ;
if(pRoot == null)return null ;
TreeNode re = KthNode(pRoot.left , k) ;
if(re != null)return re ;
num++ ;
if(num == k)return pRoot ;
return KthNode(pRoot.right , k) ;
}
}