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数据结构——单向链表

article 2024/11/13 10:25:10

链表

1.空间可以不连续（理论上长度是无限的）

2.访问元素不方便

3.链表需要更大的空间存放数据和节点地址

4.链表的插入和删除效率很高O(1)

单向链表

无头单向链表，节点插入在头的话，每次头结点都会变，所以有了有头链表，头结点的pNext总是指向链表的第一个节点

1.创建空链表

//创建空链表
LinkNode *CreateLinkList(void)
{   
    LinkNode *pTmpNode = NULL;

    pTmpNode = malloc(sizeof(LinkNode));
    if (NULL == pTmpNode)
    {
        return NULL;
    }

    pTmpNode->Data = 0;
    pTmpNode->pNext = NULL;

    return pTmpNode;
}

2.头插法

int HeadInsertLinkList(LinkNode *pHead, DataType TmpData)
{
    LinkNode *pTmpNode = NULL;

    //1.申请空间
    pTmpNode = malloc(sizeof(LinkNode));
    if (NULL == pTmpNode)
    {
        return -1;
    }

    //2.将Data成员初始化
    pTmpNode->Data = TmpData;

    //3.将pNext成员初始化(和后面连起来)
    pTmpNode->pNext = pHead->pNext;

    //4.将头结点的pNext指向新申请节点(和前面连起来)
    pHead->pNext = pTmpNode;

    return 0;
}

3.遍历

int ShowLinkList(LinkNode *pHead)
{
    LinkNode *pTmpNode = NULL;

    pTmpNode = pHead->pNext;
    while (pTmpNode != NULL)
    {
        printf("%d ", pTmpNode->Data);
        pTmpNode = pTmpNode->pNext;
    }
    printf("\n");

    return 0;
}

4.修改

int UpdateLinkList(LinkNode *pHead, DataType OldData, DataType NewData)
{
    LinkNode *pTmpNode = NULL;
    int cnt = 0;

    pTmpNode = pHead->pNext;
    while (pTmpNode != NULL)
    {
        if (pTmpNode->Data == OldData)
        {
            pTmpNode->Data = NewData;
            cnt++;
        }
        pTmpNode = pTmpNode->pNext;
    }

    return cnt;
}

5.查找

LinkNode *FindLinkList(LinkNode *pHead, DataType TmpData)
{
    LinkNode *pTmpNode = NULL;

    pTmpNode = pHead->pNext;
    while (pTmpNode != NULL)
    {
        if (pTmpNode->Data == TmpData)
        {
            return pTmpNode;
        }
        pTmpNode = pTmpNode->pNext;
    }

    return NULL;
}

6.尾插

int TailInsertLinkList(LinkNode *pHead, DataType TmpData)
{
    LinkNode *pNewNode = NULL;
    LinkNode *pTmpNode = NULL;

    pNewNode = malloc(sizeof(LinkNode));
    if (NULL == pNewNode)
    {
        return -1;
    }

    pNewNode->Data = TmpData;
    pNewNode->pNext = NULL;

    pTmpNode = pHead;
    while (pTmpNode->pNext != NULL)
    {
        pTmpNode = pTmpNode->pNext;
    }

    pTmpNode->pNext = pNewNode;

    return 0;
}

7.删除链表节点

删除链表节点，必须要知道要删节点的前一个结点，所以要定义两个指针来操作

int DeleteLinkList(LinkNode *pHead, DataType TmpData)
{
    LinkNode *pPreNode = NULL;
    LinkNode *pTmpNode = NULL;
    int cnt = 0;

    pPreNode = pHead;
    pTmpNode = pHead->pNext;
    while (pTmpNode != NULL)
    {
        if (pTmpNode->Data == TmpData)
        {
            //删除
            pPreNode->pNext = pTmpNode->pNext;
            free(pTmpNode);
            pTmpNode = pPreNode->pNext;
            cnt++;
        }
        else 
        {
            pTmpNode = pTmpNode->pNext;
            pPreNode = pPreNode->pNext;
        }
    }

    return cnt;
}

注意：free掉pTmpNode后，它变成了野指针，要为它重新赋值

8.销毁

int DestroyLinkList(LinkNode **ppHead)
{
    LinkNode *pTmpNode = NULL;
    LinkNode *pFreeNode = NULL;

    pTmpNode = pFreeNode = *ppHead;
    while (pTmpNode != NULL)
    {
        pTmpNode = pTmpNode->pNext;
        free(pFreeNode);
        pFreeNode = pTmpNode;
    }
    *ppHead = NULL;

    return 0;
}

复杂操作

1.查找链表中间节点

算法：快指针pFast每次走2步，慢指针pSlow每次走1步，快指针到达末尾时，慢指针所在的位置即为中间位置

LinkNode *FindMidLinkNode(LinkNode *pHead)
{
    LinkNode *pFast = NULL;
    LinkNode *pSlow = NULL;

    pFast = pSlow = pHead->pNext;
    while (pFast != NULL)
    {
        pFast = pFast->pNext;
        if (NULL == pFast)
        {
            break;
        }
        pFast = pFast->pNext;
        if (NULL == pFast)
        {
            break;
        }

        pSlow = pSlow->pNext;
    }

    return pSlow;
}

2.查找链表倒数第k个节点

算法：快指针先走k步，慢指针和快指针每次走1步(快指针总是领先慢指针k步)，当快指针走到末尾时,慢指针即指向链表倒数第k个节点

LinkNode *FindLastKthLinkNode(LinkNode *pHead, int k)
{
    LinkNode *pFast = pHead->pNext;
    LinkNode *pSlow = pHead->pNext;
    int i = 0;

    for (i = 0; i < k; i++)
    {
        pFast = pFast->pNext;
        if (NULL == pFast)
        {
            break;
        }
    }

    if (NULL == pFast)
    {
        return NULL;
    }

    while (pFast != NULL)
    {
        pSlow = pSlow->pNext;
        pFast = pFast->pNext;
    }

    return pSlow;
}

3.链表的倒置(反转)

算法：例如：将第头节点与第一个节点断开连接，在断开前都要保存一下头节点的下一个节点，然后向头插法一样将第一个节点插入到链表中，依次类推

int ReversalLinkList(LinkNode *pHead)
{
    LinkNode *pTmpNode = NULL;
    LinkNode *pInsertNode = NULL;

    pTmpNode = pHead->pNext;
    pHead->pNext = NULL;
    pInsertNode = pTmpNode;

    while (pTmpNode != NULL)
    {
        pTmpNode = pTmpNode->pNext;
        pInsertNode->pNext = pHead->pNext;
        pHead->pNext = pInsertNode;
        pInsertNode = pTmpNode;
    }

    return 0;
}

4.链表的排序(冒泡排序、选择排序)

冒泡排序

每轮比较之后pTmpNode1，都是下一轮的pEnd，直到pEnd = pHead->pNext->pNext;

//链表排序（冒泡排序法）
int BubbleSortLinkList(LinkNode *pHead)
{   
    LinkNode *pTmpNode1 = NULL;
    LinkNode *pTmpNode2 = NULL;
    LinkNode *pEnd = NULL;
    DataType TmpData;

    //如果链表没有节点或者只有1个节点返回0 
    if (NULL == pHead->pNext || NULL == pHead->pNext->pNext)
    {
        return 0;
    }

    while (1)
    {
        pTmpNode1 = pHead->pNext;
        pTmpNode2 = pHead->pNext->pNext;
        if (pTmpNode2 == pEnd)
        {
            break;
        }

        while (pTmpNode2 != pEnd)
        {
            if (pTmpNode1->Data > pTmpNode2->Data)
            {
                TmpData = pTmpNode1->Data;
                pTmpNode1->Data = pTmpNode2->Data;
                pTmpNode2->Data = TmpData;
            }
            pTmpNode1 = pTmpNode1->pNext;
            pTmpNode2 = pTmpNode2->pNext;
        }
        pEnd = pTmpNode1;
    }
    
    return 0;
}

选择排序：

每次选出最小的，第二小的...最大的，


//选择排序
int SelectSortLinkList(LinkNode *pHead)
{
    LinkNode *pTmpNode = NULL;
    LinkNode *pMinNode = NULL;
    LinkNode *pSwapNode = NULL;
    DataType TmpData;

    if (NULL == pHead->pNext)
    {
        return 0;
    }

    pSwapNode = pHead->pNext;

    while (pSwapNode->pNext != NULL)
    {
        pMinNode = pSwapNode;
        pTmpNode = pSwapNode->pNext;
        while (pTmpNode != NULL)
        {
            if (pTmpNode->Data < pMinNode->Data)
            {
                pMinNode = pTmpNode;
            }
            pTmpNode = pTmpNode->pNext;
        }
        if (pMinNode != pSwapNode)
        {
            TmpData = pMinNode->Data;
            pMinNode->Data = pSwapNode->Data;
            pSwapNode->Data = TmpData;
        }
        pSwapNode = pSwapNode->pNext;
    } 

    return 0;
}

5.已知链表中间某个节点地址，不知道头结点地址，如何删除该节点

算法：可以上中间这个的值变成下一个节点的值，并把它的pNext指向它的pNext->pNext,然后free掉空间

6.如何判断一个链表是否有环？环长？环的入口位置？

是否有环：快指针每次走2步,慢指针每次走1步,快慢指针相遇则说明有环

因为快指针第一次比慢指针多1，第二次快指针比慢指针快2，依次类推，环长一定是一个自然数，所以一定能相遇

如何计算环长：标记相遇的位置，让指针继续向后走，每走一步计算器自加,走回到标记位置，则计算器值即为环长
如何计算环入口位置：将一个指针从第一个节点向后走，将一个指针从相遇点向后走，两个指针相遇的位置即为环入口的位置

//判断链表是否有环
//实现方式：
//     快指针每次走2步，慢指针每次走1步
//     两者能够相遇即为有环
LinkNode *IsHasCircle(LinkNode *pHead, int *pcnt)
{
    LinkNode *pFast = NULL;
    LinkNode *pSlow = NULL;
    LinkNode *pTmpNode = NULL;
    LinkNode *pNode1 = NULL;
    LinkNode *pNode2 = NULL;
    int ret = 0;
    int cnt = 1;

    pSlow = pFast = pHead->pNext;
    while (1)
    {
        pFast = pFast->pNext;
        if (NULL == pFast)
        {
            ret = 0;
            break;
        }
        pFast = pFast->pNext;
        if (NULL == pFast)
        {
            ret = 0;
            break;
        }

        pSlow = pSlow->pNext;
        if (pSlow == pFast)
        {
            ret = 1;
            break;
        }
    }

    if (1 == ret)
    {
        //获得环长
        pTmpNode = pSlow->pNext;
        while (pTmpNode != pSlow)
        {
            cnt++;
            pTmpNode = pTmpNode->pNext;
        }
        *pcnt = cnt;

        //获得环入口位置
        pNode1 = pSlow;
        pNode2 = pHead->pNext;
        while (1)
        {
            pNode1 = pNode1->pNext;
            pNode2 = pNode2->pNext;
            if (pNode1 == pNode2)
            {
                return pNode1;
            }
        }
    }

    return NULL;
}

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