面试题
http://blog.163.com/liwangyang19880814@126/blog/static/19733528201291082432202
http://blog.csdn.net/huahuahailang/article/details/12223753
http://blog.csdn.net/g_little_boy/article/details/6483961
http://blog.csdn.net/huyfaeng/article/details/6868594
