LeetCode #19 删除链表的倒数第N个节点

/**
 * 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) {
        ListNode* p=head;
        int i=0;
        while(i<n&&p->next!=NULL){
            p=p->next;
            i++;
        }
        if(i<n){
            return head->next;
        }
        ListNode* q=head;
        while(p->next!=NULL){
            p=p->next;
            q=q->next;
        }
        q->next=q->next->next;
        return head;
    }
};