55.按之字形顺序打印二叉树

按之字形顺序打印二叉树

参与人数：1413时间限制：1秒空间限制：32768K
算法知识视频讲解

题目描述

请实现一个函数按照之字形打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，其他行以此类推。

《剑指offer》上介绍的方法太麻烦，用堆栈一会儿向左装数据，一会儿向右装数据。

我做的时候，每层数据都自右向左装入vector，装入返回值时再判断左右。

// 54.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <vector>
#include<algorithm>
using namespace::std;

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> > retVec;
if (pRoot == NULL) return retVec;

vector<TreeNode*> cur;
vector<TreeNode*> next;
int level = 0;

cur.push_back(pRoot);
while (!cur.empty() || !next.empty()) {
vector<int> tmp;
for (int i = 0; i < cur.size(); i++) {
tmp.push_back(cur[i]->val);

TreeNode* nodeTmp = cur[i];
if (nodeTmp->right)
next.push_back(nodeTmp->right);
if (nodeTmp->left)
next.push_back(nodeTmp->left);
}

if (level % 2 == 0){
std::reverse(tmp.begin(),tmp.end());
}
retVec.push_back(tmp);

cur.clear();
cur = next;
next.clear();
++level;
}
return retVec;
}

};
int _tmain(int argc, _TCHAR* argv[])
{
TreeNode p1(1);
TreeNode p2(2);
TreeNode p3(3);
TreeNode p4(4);
TreeNode p5(5);
TreeNode p6(6);
TreeNode p7(7);
TreeNode p8(8);
TreeNode p9(9);
TreeNode p10(10);
TreeNode p11(11);
TreeNode p12(12);
TreeNode p13(13);
TreeNode p14(14);
TreeNode p15(15);

p1.left = &p2;
p1.right = &p3;

p2.left = &p4;
p2.right = &p5;

p4.left = &p8;
p4.right = &p9;

p5.left = &p10;
p5.right = &p11;

p3.left = &p6;
p3.right = &p7;

p6.left = &p12;
p6.right = &p13;

p7.left = &p14;
p7.right = &p15;

Solution s;
vector<vector<int>> result = s.Print(&p1);
return 0;
}

第二次做：

/*
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>> retVec ;
vector<TreeNode*> curVec ;
vector<TreeNode*> nextVec ;
int level = 0 ;

if ( pRoot == NULL ) {
goto done ;
}

curVec.push_back( pRoot ) ;

while ( curVec.empty() == false ) {
++ level ;
vector<int> tmp ;
for ( vector<TreeNode*>::iterator it = curVec.begin(); it != curVec.end(); ++ it ) {
tmp.push_back( (*it)->val ) ;
if ( (*it)->left != NULL ) {
nextVec.push_back( (*it)->left ) ;
}
if ( (*it)->right != NULL ) {
nextVec.push_back( (*it)->right ) ;
}
}
if ( level % 2 == 0 ) {
std::reverse( tmp.begin(), tmp.end() ) ;
}
retVec.push_back( tmp ) ;
curVec.clear() ;
curVec = nextVec ;
nextVec.clear() ;
}

error :
goto done ;
done :
return retVec ;
}

};