[LintCode] 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) {
        if (head == null || n < 1){
            return head;
        }
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode preDel = dummy;
        for (int i = 0; i < n; i++){
            if (head != null){
                head = head.next;
            }
        }
        while (head != null){
            head = head.next;
            preDel = preDel.next;
        }
        preDel.next = preDel.next.next;
        return dummy.next;
    }
}