Remove Nth Node From End of List

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 (head == null) {
            return head;
        }

        ListNode dummy = new ListNode(-1);
        dummy.next = head;

        ListNode fastNode = dummy;
        ListNode slowNode = dummy;

        while (n > 0) {
            fastNode = fastNode.next;
            n--;
        }

        while (fastNode.next != null) {
            slowNode = slowNode.next;
            fastNode = fastNode.next;
        }

        if (slowNode != null && slowNode.next != null) {
            slowNode.next = slowNode.next.next;
        }

        return dummy.next;
    }
}

Hope this helps,
Michael