把二叉树打印成多行

题目描述

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) {
        //二叉树层次遍历结果
        vector<vector<int>>result;
        //二叉树当前层遍历结果
        vector<int>layer_result;
        //vector 存储当前层的结点。
        vector<TreeNode*>current_layer;
        //vector 存储下一层的结点。
        vector<TreeNode*>next_layer;

        current_layer.push_back(pRoot);
        if (pRoot == NULL) {
            return result;
        }
        while (!current_layer.empty())
        {
            layer_result.push_back(current_layer[0]->val);
            if (current_layer[0]->left != NULL) {
                next_layer.push_back(current_layer[0]->left);
            }
            if (current_layer[0]->right != NULL) {
                next_layer.push_back(current_layer[0]->right);
            }
            current_layer.erase(current_layer.begin());
            if (current_layer.empty()) {
                //二叉树下一层结点作为当前层结点
                current_layer.assign(next_layer.begin(),next_layer.end());
                //清空下一层结点结果
                next_layer.clear();
                //存储遍历当前层结果
                result.push_back(layer_result);
                //清空当前层遍历结果。
                layer_result.clear();
            }
        }
        return result;
    }

};