19. Remove Nth Node From End of List

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        if(n<=0){
            return null;
        }
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        
        ListNode predelete = dummy;
        for(int i =0; i<n;i++){
            if(head == null){
                return null;
            }
            head = head.next;
        }
        
        while(head != null){
            head = head.next;
            predelete = predelete.next;
        }
        
        predelete.next = predelete.next.next;
        return dummy.next;
        
    }
}