按之字形顺序打印二叉树
描述
给定一个二叉树，返回该二叉树的之字形层序遍历，（第一层从左向右，下一层从右向左，一直这样交替）
例如：
给定的二叉树是{1,2,3,#,#,4,5}
该二叉树之字形层序遍历的结果是
[
[1],
[3,2],
[4,5]
]
示例1
输入：
{1,2,3,#,#,4,5}
返回值：
[[1],[3,2],[4,5]]
开始我是这样写的，
public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {ArrayList<ArrayList<Integer> > result = new ArrayList<>();if (pRoot==null) {return result;}Queue<TreeNode> queue = new LinkedList<>();queue.offer(pRoot);//false奇数行，true偶数行boolean flag = false;while (queue.isEmpty()==false) {ArrayList<Integer> temp = new ArrayList<>();int size = queue.size();while (size--!=0) {TreeNode poll = queue.poll();temp.add(poll.val);if (flag==false) {if (poll.right!=null) {queue.offer(poll.right);}if (poll.left!=null) {queue.offer(poll.left);}}if (flag==true) {if (poll.left!=null) {queue.offer(poll.left);}if (poll.right!=null) {queue.offer(poll.right);}}}result.add(temp);flag=!flag;}return result;}
用例输入:{8,6,10,5,7,9,11}
预期输出:[[8],[10,6],[5,7,9,11]]
实际输出:[[8],[10,6],[9,11,5,7]]
后来看了答案，其实我是想复杂了，下面是ac代码：
import java.util.ArrayList;import java.util.LinkedList;import java.util.Queue;/*public class TreeNode {int val = 0;TreeNode left = null;TreeNode right = null;public TreeNode(int val) {this.val = val;}}*/public class Solution {public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {ArrayList<ArrayList<Integer> > result = new ArrayList<>();if (pRoot==null) {return result;}Queue<TreeNode> queue = new LinkedList<>();queue.offer(pRoot);//false奇数行，true偶数行boolean flag = false;while (queue.isEmpty()==false) {ArrayList<Integer> temp = new ArrayList<>();int size = queue.size();while (size--!=0) {TreeNode poll = queue.poll();temp.add(poll.val);if (poll.left!=null) {queue.offer(poll.left);}if (poll.right!=null) {queue.offer(poll.right);}}ArrayList<Integer> reverseList = new ArrayList<>();if (flag==true) {for (int i = temp.size()-1; i >= 0; i--) {reverseList.add(temp.get(i));}}if (flag==false) {result.add(temp);} else {result.add(reverseList);}flag=!flag;}return result;}}
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