剑指offer面试题5

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;
}



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