LeetCode Reorder List

题目：

Given a singly linked list L: L0→L1→…→Ln-1→Ln,
reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…

You must do this in-place without altering the nodes' values.

For example,
Given {1,2,3,4}, reorder it to {1,4,2,3}.

题意：

就是重新对单链表中的节点按照一定的次序进行重新排序，按照第二种方式来进行排序。此题我是采用重新新开一个ArrayList，因为采用ArrayList，相当于是数组那样排列的，而数组，是可以有下标的，从两头就可以进行往中间赶。发现这种方法也是可以过得。

public static ListNode reorderList(ListNode head)
	{
		if(head == null || head.next == null)
			return head;
		ListNode node = head;
		ArrayList<ListNode> list = new ArrayList<ListNode>();
		while(node != null)
		{
			list.add(node);
			node = node.next;
		}
		int length = list.size();
		int i = 0;
		int j = length - 1;
		int medium = length / 2;
		ListNode pre = new ListNode(-1);
		int count = 0;
		while(i <= j)
		{
			if(count % 2 == 0)
			{
				node = list.get(i);
				pre.next = node;
				if(count == 0)
					head = pre.next;
				pre = pre.next;
				i++;
			}
			else
			{
				node = list.get(j);
				pre.next = node;
				pre = pre.next;
				j--;
			}
			count++;
		}
		pre.next = null;
		return head;
	}