Improve input handling
Use two newlines after includes
Put everything in one header file
Make goal_state configurable
Put everything in one header file
Wrap long lines
Type less with using directives
Rename parameter
Remove unused operator
Refactor
Change file extensions to .cc and .h
Change names of define guards

According to the Google C++ Style Guid
Include headers without using ..
Change order of includes
Use explicit
Refactor

According to the Google C++ Style Guide
Improve error message
Refactor
Improve memory usage