[lintcode easy]Remove Nth Node From End of List

/**
 * Definition for ListNode.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int val) {
 *         this.val = val;
 *         this.next = null;
 *     }
 * }
 */ 
public class Solution {
    /**
     * @param head: The first node of linked list.
     * @param n: An integer.
     * @return: The head of linked list.
     */
    ListNode removeNthFromEnd(ListNode head, int n) {
        // write your code here
        if(head==null || n<0) return head;
        ListNode fast=head;
        ListNode slow=new ListNode(0);
        slow.next=head;
        
        while(n--!=0)
        {
            fast=fast.next;
        }
        if(fast==null)
        {
            return head.next;
        }
        while(fast!=null)
        {
            fast=fast.next;
            slow=slow.next;
            
        }
        
        ListNode next=slow.next;
        slow.next=next.next;
        
        return head;
    }
}