LeetCode Binary Tree Zigzag Level Order Traversal

题目链接：https://oj.leetcode.com/problems/binary-tree-zigzag-level-order-traversal/

题目描述：给定一棵二叉树，对其中的节点做BFS，只是每个层次的遍历顺序有着这样的要求,单数层从左到右遍历，双数层从右到左遍历，层数从1开始。

package BinaryTreeZigzagLevelOrderTraversal;

import java.util.*;
public class Solution {
class TreeNode{
int val;
TreeNode left;
TreeNode right;
TreeNode(int x){this.val=x;}
}
public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
if(root==null) return new LinkedList<List<Integer>>();
LinkedList<List<Integer>> ans = new LinkedList<List<Integer>>();

LinkedList<TreeNode> queue1 = new LinkedList<TreeNode>();
LinkedList<TreeNode> queue2 = new LinkedList<TreeNode>();
queue1.add(root);
while(!queue1.isEmpty()||!queue2.isEmpty()){
List<Integer> l1 = new LinkedList<Integer>();
List<Integer> l2 = new LinkedList<Integer>();
while(!queue1.isEmpty()){
TreeNode temp = queue1.poll();
l1.add(temp.val);
if(temp.left!=null)
queue2.add(temp.left);
if(temp.right!=null)
queue2.add(temp.right);
}
while(!queue2.isEmpty()){
TreeNode temp = queue2.poll();
l2.add(temp.val);
if(temp.left!=null)
queue1.add(temp.left);
if(temp.right!=null)
queue1.add(temp.right);
}
if(!l1.isEmpty())
ans.add(l1);
if(!l2.isEmpty())
{
LinkedList<Integer> reversed = new LinkedList<Integer>();
for(int i=l2.size()-1;i>=0;i--)
reversed.add(l2.get(i));
ans.add(reversed);
}
}
return ans;
}
}