Leetcode-Remove Nth Node From End of List

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.

AC代碼：

public class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        if( head == null ) 
			return head;
		int length = 0;
		ListNode p = head;
		ListNode q = head;
		while( p != null ){
			length++;
			p = p.next;
		}
		if( n == length ) return head.next;
		p = head;
		for( int i=0; i<n; i++ ){
			q = q.next;
		}
		while( q.next != null ){
			p = p.next;
			q = q.next;
		}
		p.next = p.next.next;
		return head;
    }
}