【剑指offer 面试题13】在 O(1) 时间删除链表结点

 #include <iostream>
 using namespace std; //构造链表结点
 struct ListNode
 {
     int val;
     ListNode *next;     ListNode(int v = ):val(v), next(NULL){};
 }; //打印结点
 void printList(ListNode *head)
 {
     while(head != NULL)
     {
         cout<<head->val<<" ";
         head = head->next;
     }
     cout<<endl;
 } //删除结点
 void deleteListNode(ListNode **head, ListNode *tobeDeleted)
 {
     //头结点或者待删除结点为空，则结束调用
     if(*head == NULL || tobeDeleted == NULL)
         return ;     //待删除结点的pnext非空，则复制其值到待删除结点，删除pnext
     if(tobeDeleted->next != NULL)
     {
         ListNode *pnext = tobeDeleted->next;         tobeDeleted->val = pnext->val;
         tobeDeleted->next = pnext->next;         delete pnext;
         pnext = NULL;
     }
     //若只剩头结点，则删除头结点
     else if(tobeDeleted == *head)
     {
         delete tobeDeleted;         tobeDeleted = NULL;
         *head = NULL;
     }
     //若待删除结点为尾结点，则顺序查找后删除
     else
     {
         ListNode *phead = *head;         while(phead->next != tobeDeleted)
         {
             phead = phead->next;
         }         phead->next = NULL;
         delete tobeDeleted;
         tobeDeleted = NULL;
     }
 } int main()
 {
     ListNode *ls = new ListNode();
     ListNode *head = ls;     ListNode *l1 = new ListNode();
     ls->next = l1;
     ls = ls->next;     ListNode *l2 = new ListNode();
     ls->next = l2;
     ls = ls->next;     ListNode *l3 = new ListNode();
     ls->next = l3;
     ls = ls->next;     ListNode *l4 = new ListNode();
     ls->next = l4;
     ls = ls->next;     cout<<"初始链表 -> ";
     printList(head);
     cout<<endl;     cout<<"删除中间结点2后 -> ";
     deleteListNode(&head,l2);
     printList(head);
     cout<<endl;     cout<<"删除尾结点4后 -> ";
     deleteListNode(&head,l4);
     printList(head);
     cout<<endl;     cout<<"删除中间结点1后 -> ";
     deleteListNode(&head,l1);
     printList(head);
     cout<<endl;     cout<<"删除尾结点3后 -> ";
     deleteListNode(&head,l1);
     printList(head);
     cout<<endl;     cout<<"删除头结点后 -> ";
     deleteListNode(&head,head);
     printList(head);
     cout<<endl;
 }

测试结果：

初始链表 ->     删除中间结点2后 ->    删除尾结点4后 ->   删除中间结点1后 ->  删除尾结点3后 -> 删除头结点后 ->