/**

* 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>>();

//List<TreeNode> templist=new ArrayList<TreeNode>();//这个list 没有实现对应接口

LinkedList<TreeNode> llist = new LinkedList<TreeNode>();//但是这个 linkedlist 实现了 deque 接口

//LinkedList<TreeNode> templist = new LinkedList<TreeNode>();//临时队列-用于存放同一排

if (root == null)return list;

llist.add(root);

TreeNode current;

while (!llist.isEmpty() ) {

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

int templen = llist.size();

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

current = llist.poll();

templist.add(current.val);

if (current.left != null)

llist.add(current.left);

if (current.right != null)

llist.add(current.right);

}

list.add(templist);

}

return list;

}

}