Rotate List 

Let's start with an example.

Given [0,1,2], rotate 1 steps to the right -> [2,0,1].

Given [0,1,2], rotate 2 steps to the right -> [1,2,0].

Given [0,1,2], rotate 3 steps to the right -> [0,1,2].

Given [0,1,2], rotate 4 steps to the right -> [2,0,1].

So, no matter how big K, the number of steps is, the result is always the same as rotating K % n steps to the right.

注意要算余数，开始我没有高明白题意，n的值要是很大大于链表的长度的话，则要算余数。