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【面试题016】反转链表

【面试题016】反转链表

定义一个函数，输入一个链表的头结点，反转该链表并且输出反转后链表的头结点；

我们定义三个指针，分别指向当前遍历到的结点，她的前一个结点，她的后一个结点；

RevList.cpp:

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#include <iostream>
#include <cstdio>
#include "List.h"

using namespace std;

ListNode *ReverseList(ListNode *pHead)
{
    ListNode *pReversedHead = NULL;
    ListNode *pNode = pHead;
    ListNode *pPrev = NULL;
    while(pNode != NULL)
    {
        ListNode *pNext = pNode->m_pNext;

//最后一个节点，让新的头指针指向他
        if(pNext == NULL)
        {
            pReversedHead = pNode;
        }

//这个指针之前左边挨着的那个节点
        pNode->m_pNext = pPrev;

        pPrev = pNode;
        pNode = pNext;
    }
    return pReversedHead;
}

// 输入的链表有多个结点
int main()
{
    ListNode *pNode1 = CreateListNode(1);
    ListNode *pNode2 = CreateListNode(2);
    ListNode *pNode3 = CreateListNode(3);
    ListNode *pNode4 = CreateListNode(4);
    ListNode *pNode5 = CreateListNode(5);

    ConnectListNodes(pNode1, pNode2);
    ConnectListNodes(pNode2, pNode3);
    ConnectListNodes(pNode3, pNode4);
    ConnectListNodes(pNode4, pNode5);

    ListNode *pHead = pNode1;
    printf("The original list is: ");
    PrintList(pHead);

    ListNode *pReversedHead = ReverseList(pHead);

    printf("The reversed list is: ");
    PrintList(pReversedHead);

    DestroyList(pReversedHead);
    return 0;
}

运行结果：

The original list is:

PrintList starts.

1 2 3 4 5

PrintList ends.

The reversed list is:

PrintList starts.

5 4 3 2 1

PrintList ends.

List.h:

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#ifndef _LIST_H_
#define _LIST_H_

struct ListNode
{
int m_nValue;
ListNode* m_pNext;
};

ListNode* CreateListNode(int value);
void ConnectListNodes(ListNode* pCurrent, ListNode* pNext);
void PrintListNode(ListNode* pNode);
void PrintList(ListNode* pHead);
void DestroyList(ListNode* pHead);
void AddToTail(ListNode** pHead, int value);
void RemoveNode(ListNode** pHead, int value);

#endif //_LIST_H_

List.cpp:

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#include "list.h"
#include <stdio.h>
#include <stdlib.h>

ListNode *CreateListNode(int value)
{
    ListNode *pNode = new ListNode();
    pNode->m_nValue = value;
    pNode->m_pNext = NULL;

    return pNode;
}

void ConnectListNodes(ListNode *pCurrent, ListNode *pNext)
{
    if(pCurrent == NULL)
    {
        printf("Error to connect two nodes. ");
        exit(1);
    }

    pCurrent->m_pNext = pNext;
}

void PrintListNode(ListNode *pNode)
{
    if(pNode == NULL)
    {
        printf("The node is NULL ");
    }
    else
    {
        printf("The key in node is %d. ", pNode->m_nValue);
    }
}

void PrintList(ListNode *pHead)
{
    printf("PrintList starts. ");

    ListNode *pNode = pHead;
    while(pNode != NULL)
    {
        printf("%d ", pNode->m_nValue);
        pNode = pNode->m_pNext;
    }

    printf(" PrintList ends. ");
}

void DestroyList(ListNode *pHead)
{
    ListNode *pNode = pHead;
    while(pNode != NULL)
    {
        pHead = pHead->m_pNext;
        delete pNode;
        pNode = pHead;
    }
}

void AddToTail(ListNode **pHead, int value)
{
    ListNode *pNew = new ListNode();
    pNew->m_nValue = value;
    pNew->m_pNext = NULL;

    if(*pHead == NULL)
    {
        *pHead = pNew;
    }
    else
    {
        ListNode *pNode = *pHead;
        while(pNode->m_pNext != NULL)
            pNode = pNode->m_pNext;

        pNode->m_pNext = pNew;
    }
}

void RemoveNode(ListNode **pHead, int value)
{
    if(pHead == NULL || *pHead == NULL)
        return;

    ListNode *pToBeDeleted = NULL;
    if((*pHead)->m_nValue == value)
    {
        pToBeDeleted = *pHead;
        *pHead = (*pHead)->m_pNext;
    }
    else
    {
        ListNode *pNode = *pHead;
        while(pNode->m_pNext != NULL && pNode->m_pNext->m_nValue != value)
            pNode = pNode->m_pNext;

        if(pNode->m_pNext != NULL && pNode->m_pNext->m_nValue == value)
        {
            pToBeDeleted = pNode->m_pNext;
            pNode->m_pNext = pNode->m_pNext->m_pNext;
        }
    }

    if(pToBeDeleted != NULL)
    {
        delete pToBeDeleted;
        pToBeDeleted = NULL;
    }
}

Makefile:

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.PHONY:clean
CPP=g++
CFLAGS=-Wall -g
BIN=test
OBJS=RevList.o List.o
LIBS=
$(BIN):$(OBJS)
    $(CPP) $(CFLAGS) $^ -o $@ $(LIBS)
%.o:%.cpp
    $(CPP) $(CFLAGS) -c $< -o $@
clean:
    rm -f *.o $(BIN)

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原文地址：https://www.cnblogs.com/codemylife/p/3708441.html