层序遍历二叉树

从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};
*/
class Solution {
public:
        vector<vector<int> > Print(TreeNode* pRoot) {
            vector<vector<int> > res;
            vector<int> temp_vec;
            queue<TreeNode*> q;
            if(pRoot==nullptr) return res;
            q.push(pRoot);
            while(!q.empty()){
                int len=q.size();
                temp_vec.clear();
                //只存每一层的queue
                while(len--){
                    TreeNode* tmp=q.front();
                    temp_vec.push_back(tmp->val);
                    q.pop();
                    if(tmp->left) q.push(tmp->left);
                    if(tmp->right) q.push(tmp->right);
                }
                res.push_back(temp_vec);
            }
            return res;
        }
    
};