【题目】

Given a binary tree, return the zigzag level order traversal of its nodes‘ values. (ie, from left to right, then right to left for the next level and alternate between).

For example:
Given binary tree {3,9,20,#,#,15,7},

    3
   /   9  20
    /     15   7

return its zigzag level order traversal as:

[
  [3],
  [20,9],
  [15,7]
]

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

【代码一】

/*********************************
*   日期：2014-12-09
*   作者：SJF0115
*   题号: Binary Tree Zigzag Level Order Traversal
*   来源：https://oj.leetcode.com/problems/binary-tree-zigzag-level-order-traversal/
*   结果：AC
*   来源：LeetCode
*   总结：
**********************************/
#include <iostream>
#include <malloc.h>
#include <stack>
#include <vector>
#include <queue>
using namespace std;

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Solution {
public:
    vector<vector<int> > zigzagLevelOrder(TreeNode *root) {
        vector<int> level;
        vector<vector<int> > levels;
        if(root == NULL){
            return levels;
        }
        queue<TreeNode*> curq,nextq;
        stack<TreeNode*> curs,nexts;
        // 第index层
        int index = 1;
        //入队列
        curq.push(root);
        // 层次遍历
        while(!curq.empty() || !curs.empty()){
            //当前层遍历
            while(!curq.empty() || !curs.empty()){
                TreeNode *p,*q;
                // 第奇数层用队列存储
                if(index & 1){
                    p = curq.front();
                    curq.pop();
                    // 第偶数层用栈存储下一层节点
                    //左子树
                    if(p->left){
                        nexts.push(p->left);
                        // 用于从左到右遍历节点
                        nextq.push(p->left);
                    }
                    //右子树
                    if(p->right){
                        nexts.push(p->right);
                        //用于从左到右遍历
                        nextq.push(p->right);
                    }
                }
                // 第偶数层用栈存储
                else{
                    p = curs.top();
                    curs.pop();
                    // 存储节点时都是从左到右遍历
                    q = curq.front();
                    curq.pop();
                    // 第奇数层用队列存储下一层节点
                    //左子树
                    if(q->left){
                        nextq.push(q->left);
                    }
                    //右子树
                    if(q->right){
                        nextq.push(q->right);
                    }
                }
                level.push_back(p->val);
            }
            index++;
            levels.push_back(level);
            level.clear();
            swap(nextq,curq);
            swap(nexts,curs);
        }//while
        return levels;
    }
};

//按先序序列创建二叉树
int CreateBTree(TreeNode* &T){
    char data;
    //按先序次序输入二叉树中结点的值（一个字符），‘#’表示空树
    cin>>data;
    if(data =http://www.mamicode.com/= '#'){>

【代码二】

[LeetCode]Binary Tree Zigzag Level Order Traversal