面试题5: 从尾到头打印链表
题目: 输入一个链表的头结点,从尾到头反过来打印出每个结点的值
预备知识:
链表结点定义:
struct ListNode
{
int m_nValue;
ListNode* m_pNext;
};
链表的操作有:创建结点,插入结点,删除结点,遍历结点等
//创建链表结点
ListNode* CreateListNode(int value)
{
ListNode* pNode = new ListNode(); //结构体起始指针(头指针)
pNode->m_nValue = value;
pNode->m_pNext = NULL;
return pNode;
}
//连接链表结点
void ConnectListNodes(ListNode* pCurrent, ListNode* pNext)
{
if(pCurrent == NULL)
{
printf("Error to connect two nodes.\n");
exit(1);
}
pCurrent->m_pNext = pNext;
}
//输出链表结点
void PrintListNode(ListNode* pNode)
{
if(pNode == NULL)
{
printf("The node is NULL\n");
}
else
{
printf("The key in node is %d.\n", pNode->m_nValue);
}
}
//遍历链表并打印
void PrintList(ListNode* pHead)
{
printf("PrintList starts.\n");
ListNode* pNode = pHead;
while(pNode != NULL)
{
printf("%d\t", pNode->m_nValue);
pNode = pNode->m_pNext;
}
printf("\nPrintList ends.\n");
}
//销毁链表(每一个结点都要销毁)
void DestroyList(ListNode* pHead)
{
ListNode* pNode = pHead;
while(pNode != NULL)
{
pHead = pHead->m_pNext; //一个一个结点的销毁
delete pNode;
pNode = pHead;
}
}
//向链表尾部添加结点
void AddToTail(ListNode** pHead, int value)
{
ListNode* pNew = new ListNode();
pNew->m_nValue = value; //初始化
pNew->m_pNext = NULL;
if(*pHead == NULL)
{
*pHead = pNew;
}
else
{ //在结点的尾部添加
ListNode* pNode = *pHead;
while(pNode->m_pNext != NULL)
pNode = pNode->m_pNext;
pNode->m_pNext = pNew;
}
}
//移去结点
void RemoveNode(ListNode** pHead, int value)
{
if(pHead == NULL || *pHead == NULL)
return;
ListNode* pToBeDeleted = NULL;
if((*pHead)->m_nValue == value) //刚好等于这个值
{
pToBeDeleted = *pHead;
*pHead = (*pHead)->m_pNext; //指针改变
}
else
{
ListNode* pNode = *pHead;
while(pNode->m_pNext != NULL && pNode->m_pNext->m_nValue != value)
pNode = pNode->m_pNext; //遍历
if(pNode->m_pNext != NULL && pNode->m_pNext->m_nValue == value) //遍历找到了这个值
{
pToBeDeleted = pNode->m_pNext;
pNode->m_pNext = pNode->m_pNext->m_pNext; //指针改变
}
}
if(pToBeDeleted != NULL)
{
delete pToBeDeleted; //销毁
pToBeDeleted = NULL;
}
}
思路:1. 把链表中结点的指针反过来,改变链表的反向,然后就可以从头到尾输出,但是该方法会改变原来链表的结果
2.根据题目的要求遍历顺序是从头到尾,而输出是从尾到头,因此可以使用栈来实现这种顺序,即通过构建一个栈(后入向出)来实现,STL中有一个stack。(显栈)
3.由于递归本质上是一个栈结构,因此可以使用递归来实现,但是当链表非常长的时候,可能导致调用栈溢出。(隐栈)
代码:
List.h
struct ListNode
{
int m_nValue;
ListNode* m_pNext;
};
//使用标识符:_declspec(dllimport)表明函数是从动态库中引入的 (孙鑫VC++ 712)
__declspec( dllexport ) ListNode* CreateListNode(int value);
__declspec( dllexport ) void ConnectListNodes(ListNode* pCurrent, ListNode* pNext);
__declspec( dllexport ) void PrintListNode(ListNode* pNode);
__declspec( dllexport ) void PrintList(ListNode* pHead);
__declspec( dllexport ) void DestroyList(ListNode* pHead);
__declspec( dllexport ) void AddToTail(ListNode** pHead, int value);
__declspec( dllexport ) void RemoveNode(ListNode** pHead, int value);
List.cpp
#include "stdafx.h"
#include "list.h"
#include <stdio.h>
#include <stdlib.h>
//创建链表结点
ListNode* CreateListNode(int value)
{
ListNode* pNode = new ListNode(); //结构体起始指针(头指针)
pNode->m_nValue = value;
pNode->m_pNext = NULL;
return pNode;
}
//连接链表结点
void ConnectListNodes(ListNode* pCurrent, ListNode* pNext)
{
if(pCurrent == NULL)
{
printf("Error to connect two nodes.\n");
exit(1);
}
pCurrent->m_pNext = pNext;
}
//输出链表结点
void PrintListNode(ListNode* pNode)
{
if(pNode == NULL)
{
printf("The node is NULL\n");
}
else
{
printf("The key in node is %d.\n", pNode->m_nValue);
}
}
//遍历链表并打印
void PrintList(ListNode* pHead)
{
printf("PrintList starts.\n");
ListNode* pNode = pHead;
while(pNode != NULL)
{
printf("%d\t", pNode->m_nValue);
pNode = pNode->m_pNext;
}
printf("\nPrintList ends.\n");
}
//销毁链表(每一个结点都要销毁)
void DestroyList(ListNode* pHead)
{
ListNode* pNode = pHead;
while(pNode != NULL)
{
pHead = pHead->m_pNext; //一个一个结点的销毁
delete pNode;
pNode = pHead;
}
}
//向链表尾部添加结点
void AddToTail(ListNode** pHead, int value)
{
ListNode* pNew = new ListNode();
pNew->m_nValue = value; //初始化
pNew->m_pNext = NULL;
if(*pHead == NULL)
{
*pHead = pNew;
}
else
{ //在结点的尾部添加
ListNode* pNode = *pHead;
while(pNode->m_pNext != NULL)
pNode = pNode->m_pNext;
pNode->m_pNext = pNew;
}
}
//移去结点
void RemoveNode(ListNode** pHead, int value)
{
if(pHead == NULL || *pHead == NULL)
return;
ListNode* pToBeDeleted = NULL;
if((*pHead)->m_nValue == value) //刚好等于这个值
{
pToBeDeleted = *pHead;
*pHead = (*pHead)->m_pNext; //指针改变
}
else
{
ListNode* pNode = *pHead;
while(pNode->m_pNext != NULL && pNode->m_pNext->m_nValue != value)
pNode = pNode->m_pNext; //遍历
if(pNode->m_pNext != NULL && pNode->m_pNext->m_nValue == value) //遍历找到了这个值
{
pToBeDeleted = pNode->m_pNext;
pNode->m_pNext = pNode->m_pNext->m_pNext; //指针改变
}
}
if(pToBeDeleted != NULL)
{
delete pToBeDeleted; //销毁
pToBeDeleted = NULL;
}
}
main.cpp
#include "stdafx.h"
#include "..\Utilities\List.h"
#include <stack> //STL: push,pop
//方法1:构建一个栈(后进先出)来实现
void PrintListReversingly_Iteratively(ListNode* pHead)
{
std::stack<ListNode*> nodes;
ListNode* pNode = pHead; //栈顶
while(pNode != NULL)
{
nodes.push(pNode); //先入栈
pNode = pNode->m_pNext; //指针向上移到
}
while(!nodes.empty())
{
pNode = nodes.top(); //栈顶
printf("%d\t", pNode->m_nValue);//先输出值
nodes.pop(); //结点出栈,同时栈顶改变
}
}
//方法2:递归本质上是一个栈结构,因此可以使用递归来实现
void PrintListReversingly_Recursively(ListNode* pHead) //层级过深,可能导致调用栈溢出
{
if(pHead != NULL)
{
if (pHead->m_pNext != NULL)
{
PrintListReversingly_Recursively(pHead->m_pNext);
}
printf("%d\t", pHead->m_nValue);
}
}
void Test(ListNode* pHead)
{
PrintList(pHead);
PrintListReversingly_Iteratively(pHead); //显示栈实现
printf("\n");
PrintListReversingly_Recursively(pHead); //隐式栈实现
}
// 1->2->3->4->5
void Test1()
{
printf("\nTest1 begins.\n");
//创建单个结点
ListNode* pNode1 = CreateListNode(1);
ListNode* pNode2 = CreateListNode(2);
ListNode* pNode3 = CreateListNode(3);
ListNode* pNode4 = CreateListNode(4);
ListNode* pNode5 = CreateListNode(5);
//连接链表结点
ConnectListNodes(pNode1, pNode2);
ConnectListNodes(pNode2, pNode3);
ConnectListNodes(pNode3, pNode4);
ConnectListNodes(pNode4, pNode5);
//测试
Test(pNode1);
//销毁栈
DestroyList(pNode1);
}
// 只有一个结点的链表: 1
void Test2()
{
printf("\nTest2 begins.\n");
ListNode* pNode1 = CreateListNode(1);
Test(pNode1);
DestroyList(pNode1);
}
// 空链表
void Test3()
{
printf("\nTest3 begins.\n");
Test(NULL);
}
int _tmain(int argc, _TCHAR* argv[])
{
Test1();
Test2();
Test3();
return 0;
}
/********************7月15日********************************/
// 面试题5.cpp : 定义控制台应用程序的入口点。
//
//面试题5:从尾到头打印链表
#include "stdafx.h"
#include <stack>
struct ListNode
{
int m_nKey;
ListNode* m_pNext;
};
/********链表的基本操作*************/
//创建结点
ListNode* CreateListNode(int value)
{
ListNode* pNode = new ListNode();
pNode->m_nKey = value;
pNode->m_pNext= NULL;
return pNode;
}
//链接结点
void ConnectListNode(ListNode* pNode1, ListNode* pNode2)
{
if(pNode1 == NULL)
return;
pNode1->m_pNext = pNode2;
}
//遍历链表
void PrintListNode(ListNode* pHead)
{
if(pHead == NULL)
return;
ListNode* pNode = pHead;
while(pNode != NULL)
{
printf("%d ", pNode->m_nKey);
pNode = pNode->m_pNext;
}
printf("\n");
}
//销毁链表
void DestroyListNode(ListNode* pHead)
{
ListNode* pNode = pHead;
while(pNode != NULL)
{
pNode = pNode->m_pNext;
delete pHead;
pHead = pNode;
}
}
/************面试题5的功能****/
void PrintListReversingly_Iteratively(ListNode* pHead)
{
std::stack<ListNode*> nodes;
ListNode* pNode = pHead;
while(pNode != NULL)
{
nodes.push(pNode); //结点入栈
pNode = pNode->m_pNext;
}
while(!nodes.empty())
{
pNode = nodes.top(); //栈顶元素
printf("%d ", pNode->m_nKey);
nodes.pop(); //出栈
}
printf("\n");
}
void PrintListReversingly_Recursively(ListNode* pHead)
{
if(pHead != NULL)
{
if(pHead->m_pNext != NULL)
PrintListReversingly_Recursively(pHead->m_pNext);
printf("%d ", pHead->m_nKey);
}
}
/***********测试链表基本功能*****************/
void Test1()
{
//创建链表结点
ListNode* pNode1 = CreateListNode(1);
ListNode* pNode2 = CreateListNode(2);
ListNode* pNode3 = CreateListNode(3);
ListNode* pNode4 = CreateListNode(4);
ListNode* pNode5 = CreateListNode(5);
ListNode* pNode6 = CreateListNode(6);
//连接链表结点
ConnectListNode(pNode1,pNode2);
ConnectListNode(pNode2,pNode3);
ConnectListNode(pNode3,pNode4);
ConnectListNode(pNode4,pNode5);
ConnectListNode(pNode5,pNode6);
//打印链表
PrintListNode(pNode1);
//销毁链表
DestroyListNode(pNode1);
}
void Test2()
{
//创建链表结点
ListNode* pNode1 = CreateListNode(1);
ListNode* pNode2 = CreateListNode(2);
ListNode* pNode3 = CreateListNode(3);
ListNode* pNode4 = CreateListNode(4);
ListNode* pNode5 = CreateListNode(5);
ListNode* pNode6 = CreateListNode(6);
//连接链表结点
ConnectListNode(pNode1,pNode2);
ConnectListNode(pNode2,pNode3);
ConnectListNode(pNode3,pNode4);
ConnectListNode(pNode4,pNode5);
ConnectListNode(pNode5,pNode6);
//打印链表
PrintListReversingly_Iteratively(pNode1);
//销毁链表
DestroyListNode(pNode1);
}
void Test3()
{
//创建链表结点
ListNode* pNode1 = CreateListNode(1);
ListNode* pNode2 = CreateListNode(2);
ListNode* pNode3 = CreateListNode(3);
ListNode* pNode4 = CreateListNode(4);
ListNode* pNode5 = CreateListNode(5);
ListNode* pNode6 = CreateListNode(6);
//连接链表结点
ConnectListNode(pNode1,pNode2);
ConnectListNode(pNode2,pNode3);
ConnectListNode(pNode3,pNode4);
ConnectListNode(pNode4,pNode5);
ConnectListNode(pNode5,pNode6);
//打印链表
PrintListReversingly_Recursively(pNode1);
printf("\n");
//销毁链表
DestroyListNode(pNode1);
}
void Test4()
{
//创建链表结点
ListNode* pNode1 = CreateListNode(1);
//打印链表
//PrintListReversingly_Iteratively(pNode1);
PrintListNode(pNode1);
//销毁链表
DestroyListNode(pNode1);
}
int _tmain(int argc, _TCHAR* argv[])
{
Test1();
Test2();
Test3();
Test4();
return 0;
}