Leetcode-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.

Note:
Given n will always be valid.
Try to do this in one pass.

Solution:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        if (head==null) return head;

        ListNode first = head;
        ListNode second = head;
        for (int i=0;i<n;i++)
            first = first.next;

        if (first==null) return second.next; 
      
        while (first.next!=null){
            second = second.next;
            first = first.next;
        }

        ListNode temp = second.next.next;
        second.next = temp;
        return head;
    }
}