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

 

class Solution {
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
        vector<vector<int> >res;
        if(root==NULL) return res;

        vector<int> level;
        queue<TreeNode* > q;
        q.push(root);

        int cnt=1;
        int curcnt=0;

        bool order=true;

        while(!q.empty())
        {
            TreeNode *node=q.front();
            q.pop();
            level.push_back(node->val);
            if(node->left)
            {
                q.push(node->left);
                curcnt++;
            }
            if(node->right)
            {
                q.push(node->right);
                curcnt++;
            }

            cnt--;
            if(cnt==0)
            {
                if(order)
                {
                    res.push_back(level);
                }else{
                    reverse(level.begin(),level.end());
                    res.push_back(level);
                }

                order=!order;
                level.clear();
                cnt=curcnt;
                curcnt=0;
            }
        }
        return res;
    }
};