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;    }}