leetcode 第一刷_Remove Nth Node From End of List

链表问题里经典的双指针，一个先动，一个后动，然后同时动，无他，但手熟尔。

class Solution {public:    ListNode *removeNthFromEnd(ListNode *head, int n) {        if(!head)            return head;        ListNode *pre = head, *end = head;        int tp = 0;        while(tp<n&&end){            tp++;            end = end->next;        }        if(tp<n)            return head;        if(tp==n&&end==NULL){            head = pre->next;            delete pre;            return head;        }else{            while(end->next){                pre = pre->next;                end = end->next;            }            ListNode *del = pre->next;            pre->next = del->next;            delete del;            return head;        }    }};