19. Remove Nth Node From End of List

Given a linked list, remove the nth 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.

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode* removeNthFromEnd(ListNode* head, int n) {        if(!head||!head->next)return NULL;//head->next不要忘加了，不然[1]数据会RE         int i=0;        ListNode *t1=head,*t2=head;        while(i++<n){            t1=t1->next;                  }        if(!t1)return head->next;//对应的测试数据 [1,2] 2         while(t1->next!=NULL){                        t1=t1->next;            t2=t2->next;        }                t2->next=t2->next->next;        return head;    }};