Binary Tree Zigzag Level Order Traversal

/**
 * 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>> result;
        if(root==nullptr) return result;
        queue<TreeNode*> q;
        q.push(root);
        int cnt=0;
        while(!q.empty()){
            int size=q.size();
            cnt++;
            vector<int> sub_result;
            for(int i=0;i<size;i++){
                TreeNode* tmp = q.front();
                q.pop();
                sub_result.push_back(tmp->val);
                if(tmp->left)q.push(tmp->left);
                if(tmp->right)q.push(tmp->right);
            }
            if(cnt%2==0)reverse(sub_result.begin(),sub_result.end());
            result.push_back(sub_result);
        }
        return result;
    }
};

思路：BFS查找，这种题目多熟悉熟悉就会做了。