Add code, not math method

[wangershi]

Using brute force to get the answer, more interesting.

[gzc]

Hi @wangershi

do you know where is exercise_code/problem-1-1.cpp

[wangershi]

@gzc Sorry, I'm not familiar with the way to pull request, it's seems that I had pull two requests, another request is in Create problem-1-1.cpp
Therefore, the request Add code, not the solve method by math is connected with Create exercise-1.2-3.cpp
If this is incorrect I'll close all those request.