2.4编写代码，以给定值x为基准将链表分割成两部分，所有小于x的结点排在大于或者等于x的结点之前。

直接创建两个链表，一个放小于x的元素，另一个链表大于或等于x的元素。

等到都分完了就合并一下。

public LinkedListNode partition(LinkedListNode node, int x)
{
    LinkedListNode beforeStart = null;
    LinkedListNode beforeEnd = null;
    LinkedListNode afterStart = null;
    LinkedListNode afterEnd = null;
    
    while (node != null)
    {
        LinkedListNode next = node.next;
        node.next = null;
        if (node.data < x)
        {
            if (beforeStart == null)
            {
                beforeStart = node;
                beforeEnd = beforeStart;
            }
            else
            {
                beforeEnd.next = node;
                beforeEnd = node;
            }
        }
        else
        {
            if (afterStart == null)
            {
                afterStart = node;
                afterEnd = afterStart;
            }
            else
            {
                afterEnd.next = node;
                afterEnd = node;
            }
        }
        node = next;
    }
    
    if (beforeStart == null)
    {
        return afterStart;
    }
    beforeEnd.next = afterStart;
    return beforeStart;    
}