Remove Nth Node From End of List

题目描述
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.

解题思路
本题要求一次遍历，想到的方法是引入一个列表保存每个节点。然后对列表中每个节点进行操作以完成对链表的修改。需要注意的是本题有很多错误校验。

相关知识点
（1）列表中删除元素

list.remove(index);//根据下标删除元素

自己的代码

package leetcode;

import java.util.ArrayList;
import java.util.List;

public class RemoveNthNodeFromEndOfList {
	public ListNode removeNthFromEnd(ListNode head, int n) {
		List<ListNode> list = new ArrayList<ListNode>();
		//处理空链表 处理空操作
		if(head == null) return null;
		if(n <= 0) return null;
		while(head != null){
			list.add(head);
			head = head.next;
		}
		//处理异常操作
		if(n > list.size()) return null;
		//如果只有一个元素
		if(list.size() == 1) return null;
		//如果删除的是尾指针
		if(n == 1){
			list.get(list.size()-2).next = null;
			return list.get(0);
		}
		//如果删除的是指针头
		if(list.size() == n) {
			list.remove(0);
			return list.get(0);
		}
		
		int index = list.size() - 1 - n;
		list.get(index).next = list.get(index + 2);
		list.remove(index + 1);
		return list.get(0);
    }
	
	public static void main(String[] args) {
		ListNode node1 = new ListNode(1);
		ListNode node2 = new ListNode(2);
		ListNode node3 = new ListNode(3);
		ListNode node4 = new ListNode(4);
		ListNode node5 = new ListNode(5);
		
		node1.next = node2;
		node2.next = node3;
		node3.next = node4;
		node4.next = node5;
		
		//int n = 2;
		//int n = 5;
		int n = 1;
		
		RemoveNthNodeFromEndOfList rnnfeol = new RemoveNthNodeFromEndOfList();
		//rnnfeol.removeNthFromEnd(node1, n).print();
		//node1.print();
		//System.out.println(rnnfeol.removeNthFromEnd(null, n));
		//System.out.println(rnnfeol.removeNthFromEnd(node1, 0));
		//System.out.println(rnnfeol.removeNthFromEnd(node1, -1));
		//System.out.println(rnnfeol.removeNthFromEnd(node1, 6));
		//System.out.println(rnnfeol.removeNthFromEnd(node5, 1));
		rnnfeol.removeNthFromEnd(node4, 1).print();
	}
}