102 Binary Tree Level Order Traversal

用队列层次遍历

/**
 * 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>> levelOrder(TreeNode* root) {
        vector<vector<int>>res;
        if(!root)return res;
        queue<TreeNode*>q;
        queue<TreeNode*>temp_q;
        q.push(root);
        while(!q.empty()){
            vector<int>temp_vec;
            temp_q=q;
            while(!q.empty())q.pop();
            while(!temp_q.empty()){
                temp_vec.push_back(temp_q.front()->val);
                if(temp_q.front()->left)q.push(temp_q.front()->left);
                if(temp_q.front()->right)q.push(temp_q.front()->right);
                temp_q.pop();
            }
            res.push_back(temp_vec);
        }
        return res;
    }
};