/in/foo.cc:6:1: error: 'stack' does not name a type
 stack<string> stk;
 ^~~~~
/in/foo.cc: In function 'void solution(std::__cxx11::string)':
/in/foo.cc:12:3: error: 'stk' was not declared in this scope
   stk.push(tmp);
   ^~~
/in/foo.cc:24:3: error: 'stk' was not declared in this scope
   stk.push(tmp);
   ^~~
/in/foo.cc:34:11: error: 'branck' was not declared in this scope
     top = branck;
           ^~~~~~
/in/foo.cc:9:9: warning: unused variable 'branch' [-Wunused-variable]
     int branch = top;
         ^~~~~~