删除单链表节点,时间复杂度为O

Posted 2020-09-30 chifandeyu

一个编程练习,删除单链表一个节点,且时间复杂度控制在O(1)内.

1.核心操作代码如下:

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

void DeleteNode(ListNode **pListHead, ListNode *pToBeDeleted)
{
    if(pListHead == NULL || pToBeDeleted == NULL)
        return;
    //=================================================
    //删除非尾节点
    if(pToBeDeleted->m_pNext != nullptr)
    {
        ListNode *temp = pToBeDeleted->m_pNext;
        pToBeDeleted->m_data = temp->m_data;
        pToBeDeleted->m_pNext = temp->m_pNext;

        delete temp;
        temp = nullptr;
    }
    //=================================================
    //只有一个节点 删除头
    else if(pToBeDeleted == *pListHead)
    {
        delete pToBeDeleted;
        pToBeDeleted = nullptr;
        *pListHead = nullptr;
    }

    //最后一种 删除节点是尾节点
    else
    {
        ListNode *cur = *pListHead;
        while (cur->m_pNext != pToBeDeleted)
        {
            cur = cur->m_pNext;
        }
        delete pToBeDeleted;
        pToBeDeleted = nullptr;
        cur->m_pNext = nullptr;
    }
}

2.完整的测试实现代码如下:

头文件

#ifndef _HEAD_H_
#define _HEAD_H_

typedef int DataType;

class ListNode
{
public:
    ListNode(const DataType & x):m_data(x), m_pNext(NULL){}

    DataType m_data;
    ListNode * m_pNext;
};

class Slist
{
public:
    Slist():m_pHead(NULL), m_pTail(NULL)
    {}

    ~Slist()
    {
        Destroy();
    }

    void Destroy()
    {
        ListNode *begin =m_pHead;
        while (begin)
        {
            ListNode *del = begin;
            begin = begin->m_pNext;
            delete del;
        }
    }
public:
    //尾插法
    void PushBack(const DataType &x)
    {
        if (m_pHead == NULL)
        {
            m_pHead = new ListNode(x);
            m_pTail = m_pHead;
        }
        else
        {
            m_pTail->m_pNext = new ListNode(x);
            m_pTail = m_pTail->m_pNext;
        }
    }
    //查找
    ListNode *find(const DataType&x)
    {
        ListNode *tmp = m_pHead;
        while (tmp != NULL)
        {
            if(tmp->m_data == x)
                return tmp;
            else
            {
                tmp = tmp->m_pNext;
            }
        }
        return NULL;
    }

    //在O(1)时间内, 删除一个节点,函数如下:
    void DeleteNodeNumone(ListNode **phead, ListNode *pToBeDelete)
    {
        if(*phead == nullptr || pToBeDelete == nullptr)
            return;
        
        if(pToBeDelete->m_pNext != nullptr)
        {
            ListNode *temp = pToBeDelete->m_pNext;
            pToBeDelete->m_data = temp->m_data;
            pToBeDelete->m_pNext = temp->m_pNext;

            delete temp;
            temp = nullptr;
        }
        //only one node
        else if(*phead == pToBeDelete)
        {
            delete pToBeDelete;
            pToBeDelete = nullptr;
            *phead = nullptr;
        }

        //删除节点是尾节点
        else
        {
            ListNode *cur = *phead;
            while (cur->m_pNext != pToBeDelete)
            {
                cur = cur->m_pNext;
            }
            delete pToBeDelete;
            pToBeDelete = nullptr;
            cur->m_pNext = nullptr;
        }
    }
    
    void print()
    {
        ListNode *begin = m_pHead;
        while (begin)
        {
            cout<<begin->m_data<<"->";
            begin = begin->m_pNext;
        }
        cout<<"NUll"<<endl;
    }
public:
    ListNode *m_pHead;
    ListNode *m_pTail;
};

#endif //_HEAD_H_

main.cpp

int main()
{
    Slist s1;
    s1.PushBack(5);
    s1.PushBack(2);
    s1.PushBack(3);
    s1.PushBack(2);
    s1.PushBack(1);
    s1.PushBack(6);
    s1.PushBack(7);
    s1.PushBack(9);
    s1.print();

    ListNode *num = s1.find(9);

    s1.DeleteNodeNumone(&s1.m_pHead, num);
    s1.print();

    num = s1.find(6);
    s1.DeleteNodeNumone(&s1.m_pHead, num);

    s1.print();
    return 0;
}

测试可以正常通过.