[Leetcode] 19. 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.

/**
 * 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(null == head)
            return null;
        
        int k = n;
        
        ListNode preHead = new ListNode(0);
        
        preHead.next = head;
        
        ListNode i = preHead;
        ListNode j = head;
        
        while(null != j.next){
            j = j.next;
            if(k > 1){
                --k;
            }else{
                i = i.next;
            }
        }
        
        i.next = i.next.next;
        
        return preHead.next;
    }
}