60.把二叉树打印成多行.md

60.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。

 

解题思路

• 这不就层序遍历吗，So Easy ！只不过要按每层来输出，普通层序遍历的话用队列即可实现，这道题要按行输出就得用两个队列。

 

代码

• C++

/*
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> > result;
            if(pRoot==NULL) return result;
            
            queue<TreeNode*> queueA;
            queue<TreeNode*> queueB;
            TreeNode* nodeTemp;
            vector<int> line;
            
            queueA.push(pRoot);
            while(!queueA.empty() || !queueB.empty()){
                line.clear();
                while(!queueA.empty()){
                    nodeTemp = queueA.front();
                    queueA.pop();
                    if(nodeTemp->left) queueB.push(nodeTemp->left);
                    if(nodeTemp->right) queueB.push(nodeTemp->right);
                    line.push_back(nodeTemp->val);
                }
                if(!line.empty()) result.push_back(line);
                
                line.clear();
                while(!queueB.empty()){
                    nodeTemp = queueB.front();
                    queueB.pop();
                    if(nodeTemp->left) queueA.push(nodeTemp->left);
                    if(nodeTemp->right) queueA.push(nodeTemp->right);
                    line.push_back(nodeTemp->val);
                }
                if(!line.empty()) result.push_back(line);
            }
            return result;
        }
    
};