Squashed commit of the following:

commit 17290fb4aaf50526484f9f79b910afe4379f2f00
Author: warmjade <sztaoyong@gmail.com>
Date:   Tue Jun 24 00:08:19 2014 -0700

    add exercise 1

commit 472d3f0cef77c773960bb2ca4f19f19e6ae23f02
Author: warmjade <sztaoyong@gmail.com>
Date:   Mon Jun 23 23:42:59 2014 -0700

    Add some comments