Leetcode 19 Remove Nth Node From End of List

Given a linked list, remove the n^th node from the end of list and return its head.

For example,

   Given linked list: 1->2->3->4->5, and n = 2.   After removing the second node from the end, the linked list becomes 1->2->3->5.

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } *///遍历两次public class Solution {    public ListNode removeNthFromEnd(ListNode head, int n) {    int length  = 0;    ListNode lis = new ListNode(0);    lis.next = head;    ListNode first = head;    while (first != null)     {        length++;        first = first.next;    }    length -= n;    first = lis;    while (length > 0)     {        length--;        first = first.next;    }    first.next = first.next.next;    return lis.next; }}