/*

* @lc app=leetcode id=102 lang=java

*

* [102] Binary Tree Level Order Traversal

*/

/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode(int x) { val = x; }

* }

*/

class Solution {

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

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

if(root == null) return list;

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

queue.offer(root);

while(!queue.isEmpty()){

int size = queue.size();

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

for(int i = 0; i < size; i++){

TreeNode node = queue.poll();

levelList.add(node.val);

if(node.left != null) queue.offer(node.left);

if(node.right != null) queue.offer(node.right);

}

list.add(levelList);

}

return list;

}

}