剑指offer--63.二叉搜索树的第k个结点

题目：给定一棵二叉搜索树，请找出其中的第k大结点（题意应该是数字索引的第k个）

分析：中序遍历，则数是从小到大排列，第k大结点，即中序结果的k-1索引值

import java.util.*;
public class wr63KthNode {
//遍历所有，输出第k-1个结点
	static ArrayList<TreeNode> list=new ArrayList<>();	
	public static TreeNode KthNode(TreeNode pRoot, int k){
		if(pRoot==null || k==0){
			return null;
		}
		inOrder(pRoot);
		if(k>list.size()){
			return null;
		}
		return list.get(k-1);
	}
	public static  void inOrder(TreeNode root){
		if(root!=null){
			inOrder(root.left);
			list.add(root);
			inOrder(root.right);
		}
	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TreeNode root=new TreeNode(5);
		TreeNode node1=new TreeNode(3);
		TreeNode node2=new TreeNode(7);
		TreeNode node3=new TreeNode(2);
		TreeNode node4=new TreeNode(4);
		TreeNode node5=new TreeNode(6);
		TreeNode node6=new TreeNode(8);
		root.left=node1;
		root.right=node2;
		node1.left=node3;
		node1.right=node4;
		node2.left=node5;
		node2.right=node6;
		
		TreeNode k=KthNode(root,3);
		System.out.print(k.val+" ");	
	}
}