leetcode103——Binary Tree Zigzag Level Order Traversal

题目大意：蛇形层次遍历二叉树

分析：bfs

代码：

/**
 * Definition for a binary tree node.
 * 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;
        if(!root) return ans;
        queue<TreeNode*> node;
        node.push(root);
        int flag = 1;
        while(!node.empty()){
            vector<int> tmp;
            int size = node.size();
            for(int i = 0;i < size;i++){
                TreeNode *now = node.front();
                node.pop();
                tmp.push_back(now->val);
                if(now->left)
                    node.push(now->left);
                if(now->right)
                    node.push(now->right);
            }
            if(flag == -1)
                reverse(tmp.begin(),tmp.end());
            ans.push_back(tmp);
            flag *= -1;
        }
        return ans;

    }
};