Reorder List

	/**
	 * 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}.
	 * 
	 * */