leetcode 19. Remove Nth Node From End of List

题目：

Given a linked list, remove the n^th node from the end of list and return its head.

For example,

   Given linked list: 1->2->3->4->5, and n = 2.   After removing the second node from the end, the linked list becomes 1->2->3->5.

Note:
Given n will always be valid.
Try to do this in one pass.

删除倒数第n个节点；

那么设定两个指针，一个fase一个slow，两个相距两个距离。

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     struct ListNode *next; * }; */struct ListNode* removeNthFromEnd(struct ListNode* head, int n) {        struct ListNode * f,*s,*t;    f=s=head;        int i;    for(i=0;i<n;i++)    {        f=f->next;        }        if(f==NULL)    {        head=head->next;        free(s);        return head;    }        while(f->next != NULL)    {        f=f->next;        s=s->next;    }            t=s->next;    s->next=t->next;    free(t);    return head;      }