【算法题】交换单链表任意两个元素

• 首先添加虚拟头结点
• 然后找到指定节点的前驱节点
• 再然后分两种情况进行交换：相邻节点交换和非相邻节点交换

#include <iostream>#include <vector>#include <numeric>#include <algorithm>using namespace std;struct ListNode{    ListNode* next;    int value;};bool List_insert(ListNode ** phead, int x, int i){//空指针    if (phead == NULL)    {        return 0;    }    ListNode * pCurrent(NULL);//头插入    if (i==1)    {        pCurrent = *phead;        ListNode * pNew = new ListNode;        pNew->value = x;        pNew->next = pCurrent;        *phead = pNew;        return 1;    }//非头插入    pCurrent = *phead;    ListNode * pfront(NULL);    int k(1);    while (k < i && pCurrent != NULL)    {        pfront = pCurrent;        pCurrent = pCurrent->next;        k++;    }    if (k != i)    {        return 0;    }    ListNode * pNew = new ListNode;    pNew->value = x;    pNew->next = pCurrent;    pfront->next = pNew;    return 1;}void List_print(ListNode * phead){    while (phead!=NULL)    {        cout << phead->value;        phead = phead->next;    }    cout << endl;}ListNode * findpre(ListNode* phead,int v)//寻找前驱节点{    if (phead==NULL)    {        return phead;    }    for (auto i = 0; i < v-1;i++)    {        if (phead!=NULL)        {            phead = phead->next;        }    }    return phead;}ListNode* swapnode(ListNode * head,int v1,int v2)//交换第v1和v2个节点{    if (head==NULL|| head->next==NULL||v1==v2)    {        return head;    }    ListNode dummy;    dummy.next = head;    if (v1>v2)    {        std::swap(v1, v2);    }    ListNode * v1_pre = findpre(&dummy, v1);    ListNode * v2_pre = findpre(&dummy, v2);    if (v2_pre == NULL||v2_pre->next == NULL)    {        return head;    }    if (v1_pre->next == v2_pre)//相邻v1 == v2_pre    {        ListNode* v2_node = v2_pre->next;        v1_pre->next = v2_node;        v2_pre->next = v2_node->next;        v2_node->next = v2_pre;    }    else    {        ListNode * v1_node = v1_pre->next;        ListNode * v2_node = v2_pre->next;        std::swap(v1_node->next, v2_node->next);        std::swap(v1_pre->next, v2_pre->next);    }    return dummy.next;}int main(){    ListNode * phead = NULL;    List_insert(&phead, 1, 1);    List_insert(&phead, 2, 1);    List_insert(&phead, 3, 1);    List_insert(&phead, 4, 1);    List_insert(&phead, 5, 1);    List_insert(&phead, 6, 1);    List_print(phead);    phead = swapnode(phead,5,7 );    List_print(phead);    phead = swapnode(phead, 5, 1);    List_print(phead);    return 0;}