【面试题017】合并两个排序的链表

【面试题017】合并两个排序的链表

两个递增排序的链表，合并这两个链表并使新链表中的结点仍然是按照递增排序的。

MergeList.cpp:

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

using namespace std;

ListNode *Merge(ListNode *pHead1, ListNode *pHead2)
{
    if(pHead1 == NULL)
    {
        return pHead2;
    }
    else if(pHead2 == NULL)
    {
        return pHead1;
    }

    ListNode *pMergeHead = NULL;
    if(pHead1->m_nValue < pHead2->m_nValue)
    {
        pMergeHead = pHead1;
        pMergeHead->m_pNext = Merge(pHead1->m_pNext, pHead2);
    }
    else
    {
        pMergeHead = pHead2;
        pMergeHead->m_pNext = Merge(pHead1, pHead2->m_pNext);
    }
    return pMergeHead;
}

// ====================测试代码====================
ListNode *Test(char *testName, ListNode *pHead1, ListNode *pHead2)
{
    if(testName != NULL)
        printf("%s begins: ", testName);

    printf("The first list is: ");
    PrintList(pHead1);

    printf("The second list is: ");
    PrintList(pHead2);

    printf("The merged list is: ");
    ListNode *pMergedHead = Merge(pHead1, pHead2);
    PrintList(pMergedHead);
    return pMergedHead;
}

// list1: 1->3->5
// list2: 2->4->6
int main()
{
    ListNode *pNode1 = CreateListNode(1);
    ListNode *pNode3 = CreateListNode(3);
    ListNode *pNode5 = CreateListNode(5);

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

    ListNode *pNode2 = CreateListNode(2);
    ListNode *pNode4 = CreateListNode(4);
    ListNode *pNode6 = CreateListNode(6);

    ConnectListNodes(pNode2, pNode4);
    ConnectListNodes(pNode4, pNode6);

    ListNode *pMergedHead = Test("Test1", pNode1, pNode2);

    DestroyList(pMergedHead);
    return 0;
}

运行结果：

Test1 begins:

The first list is:

PrintList starts.

1 3 5

PrintList ends.

The second list is:

PrintList starts.

2 4 6

PrintList ends.

The merged list is:

PrintList starts.

1 2 3 4 5 6

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=MergeList.o List.o
LIBS=
$(BIN):$(OBJS)
    $(CPP) $(CFLAGS) $^ -o $@ $(LIBS)
%.o:%.cpp
    $(CPP) $(CFLAGS) -c $< -o $@
clean:
    rm -f *.o $(BIN)