「LeetCode」19. 删除链表的倒数第 N 个结点

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode hair =new ListNode(-1,head);
        ListNode P =head, Q =hair;
        while (n-- >0) {
            P = P.next;
        }
        while (P !=null) {
            P =P.next;
            Q =Q.next;
        }
        Q.next =Q.next.next;
        return hair.next;
    }
}