Remove Nth Node From End of List

1. Problem

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

For 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.
Try to do this in one pass.

2. Solution

/**
* 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( head == null )
return head;
//create a new head node so that we can always remove p.next
ListNode newHead = new ListNode(0);
newHead.next = head;
ListNode p = newHead;   //point to the previous node before to-be-deleted node
ListNode q = head;  //q - p = n;
int count = 1;  //to find the first satisfied q;
for( ; q.next!=null && count<n; count++, q = q.next);
//the to-be-deleted node exists
if(count == n ){
while( q.next != null ){
p = p.next;
q = q.next;
}
p.next = p.next.next;
}
return newHead.next;
}
}