【LeetCode】删除链表的倒数第N个节点【双指针法】

/**
 * 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 k)
{
    if(head==NULL)
        return NULL;
    if(head->next==NULL&&k==1)
        return NULL;
    ListNode *p1=head,*p2=head,*pre=head;
    int c=k-1;
    while(c--)
    {
        p2=p2->next;
    }
    while(p2->next!=NULL)
    {
        pre=p1;
        p1=p1->next;
        p2=p2->next;
    }
    if(p1==head)
        return p1->next;
    else
    {
        pre->next=p1->next;
    }
    return head;
}
};