Merge pull request #4 from raulchen/master

update week3 problems
gaoqiang weekly code 2 commit
Create chenxi.cpp
Create chenxi.cpp
Merge pull request #5 from raulchen/master

upload week3 code by chenhao
Create wufan.cpp
Create wufan.cpp
Create wufan.cpp
Create wufan.cpp
Create chenxi.cpp
Update plan.md
Merge pull request #2 from coderfengyun/master

0428 week3