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package byteDance;

import java.util.ArrayList;

import java.util.List;

import java.util.Stack;

/**

* Created by lizeyang on 2020/5/16.

* 二叉排序树找第k大的元素

*/

public class test42 {

//利用二叉搜索树的特点，左<中<右，再利用中序排序即可

public static int test(TreeNode root, int k) {

if (root == null) {

return 0;

}

Stack<TreeNode> stack = new Stack<>();

List<Integer> list = new ArrayList<>();

while (!stack.isEmpty() || root != null) {

if (root != null) {

stack.push(root);

root = root.left;

} else {

root = stack.pop();

list.add(root.val);

root = root.right;

}

}

if (k > list.size() || k < 0) {

return 0;

}

return list.get(list.size() - k);

}

public static void main(String[] args) {

TreeNode root = new TreeNode(5);

root.left = new TreeNode(4);

root.right = new TreeNode(8);

root.left.left = new TreeNode(3);

root.right.left = new TreeNode(7);

root.right.left.left = new TreeNode(6);

root.right.right = new TreeNode(9);

System.out.println(test(root, 5));

}

}