q19_删除链表的倒数第N个节点

public class ListNode {
    int val;
    ListNode next;
    ListNode(int x) {
        val = x;
    }
}
/**
 * 利用两个指针 o(n)
 */
public class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode first = dummy;
        ListNode second = dummy;
        for (int i = 1; i <= n + 1; i++) {
            first = first.next;
        }
        while (first != null) {
            first = first.next;
            second = second.next;
        }
        second.next = second.next.next;
        return dummy.next;
    }
}