[leetcode] Remove Nth Node From End of List

/**
* 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==nullptr){
return nullptr;
}
ListNode *fast,*slow;
fast=slow=head;

for(int i=1;i<=n;i++){//快指针先走n步
fast=fast->next;
}
if(fast==nullptr){//快指针走到了末尾
return head->next;
}
while(fast->next!=nullptr){//快慢指针一起走
fast=fast->next;
slow=slow->next;
}
slow->next=slow->next->next;
return head;
}
};