[C++] 「LeetCode」19. 删除链表的倒数第 N 个结点

• 删除链表的倒数第 N 个结点
  给你一个链表，删除链表的倒数第 n 个结点，并且返回链表的头结点。
  

/**
 * 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;
  }
}