Remove Nth Node From End of List

给一个linked list和一个数, 删除list后边n个node. 这个用双指针经典做法

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode pre = head;
        ListNode cur = head;
        ListNode next = head;
        for(int i = 0 ; i < n ; i++){
            next = next.next;
        }
        while(next != null) {
            pre = cur;
            cur = cur.next;
            next = next.next;
        }
        if(cur == head && next == null)
            head = head.next;
        pre.next = cur.next;
        return head;
    }
}