[LeetCode]Binary Tree Zigzag Level Order Traversal

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]
]

这道题是在Binary Tree Level Order Traversal的基础上多了一个条件：相邻两层的“左-右”顺序相反。增设一个变量level用来记录第几层，当level为偶数时，将temp中的元素反转即可。
下面贴上代码：

/**
 * Definition for binary tree
 * 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<vector<int> > ans;
        queue<TreeNode*> q;
        if (root == NULL)
            return ans;
        q.push(root);
        int nextCount = 0;
        int curCount = 1;
        int level = 0;
        vector<int> temp;
        while (!q.empty()){
            TreeNode* p = q.front();
            q.pop();
            temp.push_back(p->val);
            if (p->left){
                q.push(p->left);
                nextCount++;
            }
            if (p->right){
                q.push(p->right);
                nextCount++;
            }
            curCount--;
            if (!curCount){
                level++;
                if (level % 2 == 0){
                    reverse(temp.begin(),temp.end());
                }
                ans.push_back(temp);
                temp=vector<int>();
                curCount = nextCount;
                nextCount = 0;
            }
        }
        return ans;
    }
};