C++ 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>> printFromTopToBottom(TreeNode* root) {

        vector<vector<int> >res;
        if(!root)return  res;

        queue<TreeNode*>q,child;
        vector<int>line;

        q.push(root);

        while(q.size()){
            auto t=q.front();

            line.push_back(t->val);
            //printf("%d",t->val);

            if(t->left){
                child.push(t->left);
            }

            if(t->right){
                child.push(t->right);
            }
             q.pop();

            if(q.empty()){
                while(child.size()){
                //cout<<endl;


                auto m=child.front();
                q.push(m);
                child.pop();
                }
                res.push_back(line);
                line.clear();
            }
        }

        return res;
    }
};