Remove Nth Node From End of List

题目连接：http://www.leetcode.com/onlinejudge

Given a linked list, remove the n^th 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.

public class Solution {    public ListNode removeNthFromEnd(ListNode head, int n) {        // Start typing your Java solution below        // DO NOT write main() function            if(head == null) return null;            int i = 0;    ListNode phead = head;    ListNode prevhead = head;        while(i++ < n)    {    phead = phead.next;    }        while(phead != null && phead.next != null)    {    head = head.next;    phead = phead.next;    }        if(phead == null) return prevhead.next;    head.next = head.next.next;        return prevhead;    }}