LeetCode OJ - Remove Nth Node From End of List

public class Solution { 

    public ListNode removeNthFromEnd(ListNode head, int n) { 

        // Note: The Solution object is instantiated only once and is reused by each test case. 

        if(head == null) 

            return null; 

        ListNode p = head; 

        ListNode q = head; 

        for(int i = 0; i < n; i++) 

        { 

            q = q.next; 

        } 

        if(q == null) 

        { 

            head = head.next; 

            p = null; 

            return head; 

        } 

        while(q.next != null) 

        { 

            p = p.next; 

            q = q.next; 

        } 

        ListNode tmp = p.next.next; 

        p.next = tmp; 

        return head; 

           

    } 

}