【LeetCode-剑指offer】-- 21.删除链表的倒数第N个结点

21.删除链表的倒数第N个结点

方法：计算链表长度

/**
 * 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 dummy = new ListNode(0,head);
        ListNode p = head;
        int m = 0;
        while(p != null){
            p = p.next;
            m++;
        }
        int x = m - n ;
        ListNode q = dummy;
        while(x > 0){
            q = q.next;
            x--;
        }
        q.next = q.next.next;
        return dummy.next;
    }
}