Remove Nth Node from End of List

题目：

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

Given linked list: 1->2->3->4->5->null, and n = 2.
After removing the second node from the end, 
the linked list becomes 1->2->3->5->null.

分析：

画图确定特殊情况

解法：

public class Solution {
    /**
     * @param head: The first node of linked list.
     * @param n: An integer.
     * @return: The head of linked list.
     */
    ListNode removeNthFromEnd(ListNode head, int n) {
        // write your code here
        if (n <= 0) {
            return head;
        }
        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        ListNode slow = dummy;
        ListNode fast = dummy;
        for (int i = 0; i < n; i++) {
            fast = fast.next;
            if (fast == null) {
                return dummy.next;
            }
        }
        while (fast.next != null) {
            slow = slow.next;
            fast = fast.next;
        }
        slow.next = slow.next.next;
        return dummy.next;
    }
}