143. 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}.

解题思路

见程序注释