剑指Offer算法实现之十三：在O(1)时间删除链表节点

题目：给定单向链表的头指针和一个节点指针，定义一个函数在O(1)时间删除该节点。链表节点与函数定义如下：

struct ListNode{    int m_nValue;    ListNode *m_pNext;};void DeleteNode(ListNode **pListHead, ListNode *pToBeDeleted);

思路：

①单向链表，若按照常规思路，即使待删除节点的前继(若有)指向待删除节点的后继(若有)。搜索前继则需要O(n)时间
②可考虑逻辑删除。实际应用中(题目中给出的定义仅为示例)，链表节点往往是通过指针指向实际被“链接”的数据，拷贝的成本很低。若有后继，则将后继数据拷贝至待删除节点N，再将后继物理删除。若无后继，则按照①中作物理删除。

编译环境：ArchLinux+Clang3,3，C++11

实现：

#include <iostream>#include <list>using namespace std;struct ListNode{    int m_nValue;    ListNode *m_pNext;};void DeleteNode(ListNode **pListHead, ListNode *pToBeDeleted){    if (!pListHead || !pToBeDeleted)        return;    if (pToBeDeleted->m_pNext) { // 删除节点非节点        ListNode *ptr = pToBeDeleted->m_pNext;        pToBeDeleted->m_nValue = ptr->m_nValue;        pToBeDeleted->m_pNext = ptr->m_pNext;        delete ptr;    } else if (*pListHead == pToBeDeleted) { // 删除尾节点，删除后链表为空        *pListHead = pToBeDeleted->m_pNext;        delete pToBeDeleted;    } else { // 删除尾节点，删除后链表非空        ListNode *prev = *pListHead;        while (prev->m_pNext != pToBeDeleted) {            prev = prev->m_pNext;        }        prev->m_pNext = nullptr;        delete pToBeDeleted;    }}void printList(ListNode *phead){    ListNode *pNode = phead;    while (pNode) {        cout << pNode->m_nValue << '\t';        pNode = pNode->m_pNext;    }    if (phead)        cout << endl;}int main(){    list<int> a{1,2,3};    a.reverse();    ListNode *phead = nullptr;    for (auto i : a) { //构造链表1,2,3        phead = new ListNode{i, phead};    }    printList(phead);    DeleteNode(&phead, phead->m_pNext);    printList(phead);    DeleteNode(&phead, phead->m_pNext);    printList(phead);    DeleteNode(&phead, phead);    printList(phead);}