Reverse a linked list iteratively, do it first with single pointers and then
do it again with double pointers. Now do it again recursively but not tail-
recursive, and then do it again tail-recursively. What do you do if it has a
loop? http://cpuzz.blogspot.com/2005/07/reverse-single-linked-list-using.html
第一个问题的解，真要是面的时候给问到，脑子一下没转过弯来，肯定答不出来。。。
