《剑指offer》面试题13—O(1)时间删除链表结点

题目：给定单向链表的头指针和某结点指针，实现函数在O(1)时间内删除指定节点。

思路：由于没有要删除结点（j结点）的前一个结点（i结点）指针，通常想法是从头开始遍历找到指定结点的前一个结点（i结点），然后使i结点的指针指向j结点的后一个结点k结点。但是这样是O(n)的时间复杂度，不符合要求。

解决方法很巧妙：由于有要删除的j结点的指针，因此可以很容易得到j结点的后一个结点k结点的指针，只要把k结点的内容复制给i结点，然后删除k结点即可。

但是要注意！如果链表只有一个结点，head指针要指NULL；如果要删除的是尾结点，即后面没有结点了，那么也只能从头开始遍历。

  1 #include <iostream>
  2 using namespace std;
  3 
  4 
  5 class Node
  6 {
  7 public:
  8     Node(int v, Node* n)
  9     {val = v;
 10     next = n;}
 11     ~Node(){}
 12     int val;
 13     Node* next;
 14 };
 15 Node * phead = NULL;
 16 
 17 void AddNode(int val)
 18 {
 19     Node* pnode = new Node(val,NULL);
 20     //Node one_node(val,NULL); 这里有大bug！如果这样写，在函数退出时自动调用析构函数！链表就乱了！
 21     if(phead == NULL)
 22     {
 23         phead = pnode;
 24     }
 25     else
 26     {
 27         Node* p = phead;
 28         while(p->next != NULL)
 29         {
 30             p = p->next;
 31         }
 32         p->next = pnode;
 33     }
 34 }
 35 void PrintLink()
 36 {
 37     Node* p = phead;
 38     while(p != NULL)
 39     {
 40         int temp = p->val;
 41         cout<<temp<<endl;
 42         p = p->next;
 43     }
 44 }
 45 void DeleteNode(Node* pdelete)
 46 {
 47     Node * p;
 48     if(phead == NULL || pdelete == NULL)   //check
 49         return;
 50 
 51     if(pdelete == phead)  //the node to be deleted is equal to the head
 52     {
 53         if(phead->next == NULL)//only one node
 54         {
 55             delete pdelete;
 56             pdelete = NULL;
 57             phead = NULL;
 58         }
 59         else        //more than one node
 60         {
 61             phead = phead->next;
 62             delete pdelete;
 63             pdelete = NULL;
 64         }
 65     }
 66     else if(pdelete->next == NULL) //the node to be deleted is the last node
 67     {
 68         p = phead;
 69         while (p->next->next != NULL) p = p->next;  //find the node before the last node
 70         p->next = NULL;
 71         delete pdelete;
 72         pdelete = NULL;
 73     }
 74     else //the normal situation,not the head or the tail
 75     {
 76         Node* pnext = pdelete->next;
 77         pdelete->val = pnext->val;
 78         pdelete->next = pnext->next;
 79         delete pnext;
 80         pnext = NULL;
 81     }
 82 }
 83 
 84 int main()
 85 {
 86     int val,del,flag;
 87     Node* pdelete;
 88     cin>>val;
 89     while(val != 0)
 90     {
 91         AddNode(val);
 92         cin>>val;
 93     }
 94     PrintLink();
 95 
 96     cout<<"Input the node number you want to delete:"<<endl;
 97     cin>>del;
 98 
 99     pdelete = phead;
100     if(phead == NULL) cout<<"No node!"<<endl;
101 
102     flag = 1;
103     for(int i=0;i<del&&flag;i++)
104     {
105         if (pdelete->next!=NULL) pdelete = pdelete->next;
106         else
107         {
108             cout << "The node not exists!"<<endl;
109             flag=0;
110         }
111     }
112     if(flag) DeleteNode(pdelete);
113     PrintLink();
114 
115     return 0;
116 }
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posted on 2013-09-07 22:22  CnZyy  阅读(414)  评论(0)  编辑  收藏  举报

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