Leetcode 19 Remove Nth Node From End of List

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;
}
}