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.
有一种用栈的做法 参考  https://github.com/ds-sww/codebase/blob/master/TA/assignment4/POJ2559/main.cpp