Create Partition List 

Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.

You should preserve the original relative order of the nodes in each of the two partitions.

For example,
Given 1->4->3->2->5->2 and x = 3,
return 1->2->2->4->3->5.

开始想复杂了。后来发现题意后，其实不难。两个链表一个指向少的，一个指向多的，最后合并。不过会浪费空间，以空间换时间。