合并两个有序链表

1.非递归方式

#include "stdafx.h"
#include <iostream>
using namespace std;

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

//合并两个有序链表,非递归方法
ListNode *MergeTwoList(ListNode *pListOneHead, ListNode *pListTwoHead)
{
if (pListOneHead == NULL)
{
return pListTwoHead;
}

if (pListTwoHead == NULL)
{
return pListOneHead;
}

ListNode *pNode1 = pListOneHead;
ListNode *pNode2 = pListTwoHead;
ListNode *pMergeListHead = NULL;
ListNode *pCurLastNode = NULL;

if (pNode1->m_nValue < pNode2->m_nValue)
{    
pMergeListHead = pListOneHead;
pNode1 = pNode1->m_pNext;
pCurLastNode = pMergeListHead;
}
else
{
pMergeListHead = pListTwoHead;
pNode2 = pNode2->m_pNext;
pCurLastNode = pMergeListHead;
}

while (pNode1 != NULL && pNode2 != NULL)
{
if (pNode1->m_nValue < pNode2->m_nValue)
{    
pCurLastNode->m_pNext = pNode1;
pCurLastNode = pNode1;
pNode1 = pNode1->m_pNext;    
}
else
{
pCurLastNode->m_pNext = pNode2;
pCurLastNode = pNode2;
pNode2 = pNode2->m_pNext;    
}

if (pNode1 == NULL)
{
pCurLastNode->m_pNext = pNode2;    
}

if (pNode2 == NULL)
{
pCurLastNode->m_pNext = pNode1;    
}
}

return pMergeListHead;
}

//创建一个链表，输入从头到尾结点的值，输入-1表示结束
void CreateList(ListNode *& pHead)
{    
ListNode *pListNode = NULL;
ListNode *pCurLastNode = NULL;
bool isHead = true;

while (1)
{
if (isHead)
{    
pHead = new ListNode();
cin >> pHead->m_nValue;
if (pHead->m_nValue == -1)
{
pHead = NULL;
break;
}
pHead->m_pNext = NULL;
isHead = false;
pCurLastNode = pHead;
}
else
{
pListNode = new ListNode();
cin >> pListNode->m_nValue;
if (pListNode->m_nValue == -1)
{
break;
}
pListNode->m_pNext = NULL;
pCurLastNode->m_pNext = pListNode;
pCurLastNode = pListNode;    
}    
}
}

//从头到尾打印链表
void PrintList(ListNode *&pHead)
{
if (pHead != NULL)
{
ListNode *pCur = pHead;
while (pCur != NULL)
{
cout << pCur->m_nValue << " ";
pCur = pCur->m_pNext;
}
cout << endl;
}
else
{
cout << "链表为空！" << endl;
}
}

int _tmain(int argc, _TCHAR* argv[])
{
ListNode *pList1Head = NULL;
CreateList(pList1Head);
PrintList(pList1Head);

ListNode *pList2Head = NULL;
CreateList(pList2Head);
PrintList(pList2Head);

ListNode *pMergeListHead = MergeTwoList(pList1Head, pList2Head);
if (pMergeListHead != NULL)
{
cout << pMergeListHead->m_nValue << endl;
}    
PrintList(pMergeListHead);

system("pause");
return 0;
}

2.递归方式

#include "stdafx.h"
#include <iostream>
using namespace std;

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

//合并两个有序链表,递归方法
ListNode *MergeTwoList(ListNode *pListOneHead, ListNode *pListTwoHead)
{
    if (pListOneHead == NULL)
    {
        return pListTwoHead;
    }

    if (pListTwoHead == NULL)
    {
        return pListOneHead;
    }

    ListNode *pMergeListHead = NULL;

    if (pListOneHead->m_nValue < pListTwoHead->m_nValue)
    {
        pMergeListHead = pListOneHead;
        pMergeListHead->m_pNext = MergeTwoList(pMergeListHead->m_pNext, pListTwoHead);
    }
    else
    {
        pMergeListHead = pListTwoHead;
        pMergeListHead->m_pNext = MergeTwoList(pListOneHead, pMergeListHead->m_pNext);
    }

    return pMergeListHead;
}

//创建一个链表，输入从头到尾结点的值，输入-1表示结束
void CreateList(ListNode *& pHead)
{    
    ListNode *pListNode = NULL;
    ListNode *pCurLastNode = NULL;
    bool isHead = true;

    while (1)
    {
        if (isHead)
        {    
            pHead = new ListNode();
            cin >> pHead->m_nValue;
            if (pHead->m_nValue == -1)
            {
                pHead = NULL;
                break;
            }
            pHead->m_pNext = NULL;
            isHead = false;
            pCurLastNode = pHead;
        }
        else
        {
            pListNode = new ListNode();
            cin >> pListNode->m_nValue;
            if (pListNode->m_nValue == -1)
            {
                break;
            }
            pListNode->m_pNext = NULL;
            pCurLastNode->m_pNext = pListNode;
            pCurLastNode = pListNode;    
        }            
    }
}

//从头到尾打印链表
void PrintList(ListNode *&pHead)
{
    if (pHead != NULL)
    {
        ListNode *pCur = pHead;
        while (pCur != NULL)
        {
            cout << pCur->m_nValue << " ";
            pCur = pCur->m_pNext;
        }
        cout << endl;
    }
    else
    {
        cout << "链表为空！" << endl;
    }
}

int _tmain(int argc, _TCHAR* argv[])
{
    ListNode *pList1Head = NULL;
    CreateList(pList1Head);
    PrintList(pList1Head);

    ListNode *pList2Head = NULL;
    CreateList(pList2Head);
    PrintList(pList2Head);

    ListNode *pMergeListHead = MergeTwoList(pList1Head, pList2Head);
    if (pMergeListHead != NULL)
    {
        cout << pMergeListHead->m_nValue << endl;
    }    
    PrintList(pMergeListHead);

    system("pause");
    return 0;
}