Remove Nth Node From End of List - LeetCode

Given a linked list, remove the n-th node from the end of list and return its head.

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.

Follow up:

Could you do this in one pass?

Java Solution :

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