打印二叉树成多行

思路：简单的层序遍历

/*
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) {
            if(!pRoot)return {};
            vector<vector<int>> v;
            queue<TreeNode*> q;
            q.push(pRoot);
            while(!q.empty()){
                vector<int> t;
                int size = q.size();
                while(size--){
                    TreeNode* tmp = q.front();
                    q.pop();
                    t.push_back(tmp->val);
                    if(tmp->left)
                        q.push(tmp->left);
                    if(tmp->right)
                        q.push(tmp->right);
                }
                v.push_back(t);
            }
            return v;
        }
    
};