【剑指offer 面试题15】链表中倒数第K个结点

思路：

　　定义两个指针同时指向head，第一个指针先走K-1步，随后二个指针同时移动，当第一个指针到末尾处时，第二个指针所指向的即为倒数第K个结点。

 

 1 #include <iostream>
 2 using namespace std;
 3 
 4 struct ListNode
 5 {
 6     int val;
 7     ListNode *next;
 8     ListNode(int v = 0):val(v), next(NULL){}
 9 };
10 
11 ListNode *findLastKthnumber(ListNode **pListHead, unsigned int k)
12 {
13     if(*pListHead == NULL || k == 0)
14         return NULL;
15 
16     ListNode *pFirst = *pListHead;
17     ListNode *pSecond = *pListHead;
18 
19     for(int i = 0; i < k - 1; i++)
20     {
21         pFirst = pFirst->next;
22         if(pFirst == NULL)
23             return NULL;
24     }
25 
26     while(pFirst->next != NULL)
27     {
28         pFirst = pFirst->next;
29         pSecond = pSecond->next;
30     }
31 
32     return pSecond;
33 }
34 
35 int main()
36 {
37     ListNode *first = new ListNode(1);
38     ListNode *head = first;
39 
40     ListNode *second = new ListNode(2);
41     first->next = second;
42     first = first->next;
43 
44     ListNode *third = new ListNode(3);
45     first->next = third;
46     first = first->next;
47 
48     cout<<"初始链表： ";
49     ListNode *print = head;
50     while(print != NULL)
51     {
52         cout<<print->val<<"  ";
53         print = print->next;
54     }
55     cout<<endl<<endl;
56 
57     cout<<"倒数第零个结点： ";
58     ListNode *res = findLastKthnumber(&head, 0);
59     if(res != NULL)
60         cout<<res->val<<endl;
61     else
62         cerr<<"error!"<<endl;
63 
64     cout<<"倒数第一个结点： ";
65     res = findLastKthnumber(&head, 1);
66     if(res != NULL)
67         cout<<res->val<<endl;
68     else
69         cerr<<"error!"<<endl;
70 
71     cout<<"倒数第二个结点： ";
72     res = findLastKthnumber(&head, 2);
73     if(res != NULL)
74         cout<<res->val<<endl;
75     else
76         cerr<<"error!"<<endl;
77 
78     cout<<"倒数第三个结点： ";
79     res = findLastKthnumber(&head, 3);
80     if(res != NULL)
81         cout<<res->val<<endl;
82     else
83         cerr<<"error!"<<endl;
84 
85     cout<<"倒数第四个结点： ";
86     res = findLastKthnumber(&head, 4);
87     if(res != NULL)
88         cout<<res->val<<endl;
89     else
90         cerr<<"error!"<<endl;
91 }

 

测试结果：

初始链表： 1  2  3

倒数第零个结点： error!
倒数第一个结点： 3
倒数第二个结点： 2
倒数第三个结点： 1
倒数第四个结点： error!

 

posted @ 2015-06-21 14:08  tjuloading  阅读(140)  评论(0)    收藏  举报