13307130254_LIANGYONGQING_ASSIGNMENT3 & 4 DONE.

Assignment3 & Assignment4 done. I was too tired to finish AC zidongji.
Because of some mistakes, I need to re update assignment1 & 2.
还有一用两个栈模拟队列的方法，我觉得很好。你可以看看。 忘了在哪里看到的= =，自己到代码堆里找吧，正好读读别人代码 ^_^