package self;

import java.util.ArrayList;

import java.util.Collections;

import java.util.LinkedList;

import java.util.List;

/**

* @author qiaoying

* @date 2019-04-26 11:08

*/

public class LevelOrder {

public List<List<Integer>> levelOrder(TreeNode root) {

LinkedList<TreeNode> queue = new LinkedList<>();

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

if (root == null) {

return result;

}

queue.add(root);

while (!queue.isEmpty()) {

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

for (TreeNode t:queue

) {

tmp.add(t.val);

}

result.add(tmp);

int count = queue.size();

while (count > 0) {

TreeNode node = queue.poll();

if (node.left != null) {

queue.add(node.left);

}

if (node.right != null) {

queue.add(node.right);

}

count--;

}

}

return result;

}

public static void main(String[] args) {

TreeNode treeNode1 = new TreeNode(3);

TreeNode treeNode2 = new TreeNode(9);

TreeNode treeNode3 = new TreeNode(20);

TreeNode treeNode4 = new TreeNode(15);

TreeNode treeNode5 = new TreeNode(7);

treeNode1.left = treeNode2;

treeNode1.right = treeNode3;

treeNode3.left = treeNode4;

treeNode3.right = treeNode5;

LevelOrder levelOrder = new LevelOrder();

List<List<Integer>> result = levelOrder.levelOrder(treeNode1);

Collections.reverse(result);

System.out.println(result);

}

}