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;
}
};