二叉搜索树的第K个节点

package 二叉搜索树的第K个节点;

import java.util.ArrayDeque;
import java.util.Stack;

/**
* Created by h on 16-12-25.
*/
class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;

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

}

}

public class Solution {

TreeNode KthNode(TreeNode pRoot, int k) {
if (pRoot == null) {
return null;
}
Stack<TreeNode> s = new Stack<>();
inOrder(pRoot, s);
while (--k != 0) {
if (!s.isEmpty()) {
s.pop();
} else {
return null;
}
}
if (s.isEmpty()) return null;
else return s.peek();
}

private void inOrder(TreeNode pRoot, Stack<TreeNode> ad) {
if (pRoot == null) {
return;
}
inOrder(pRoot.right, ad);
ad.push(pRoot);
inOrder(pRoot.left, ad);

}

public static void main(String[] args) {
//new Solution().KthNode()
}
}