Compilare: main.cpp: In function 'int solve2(const string&)': main.cpp:19:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 19 | for (int i = 1; i != s.size(); ++ i) { | ~~^~~~~~~~~~~ main.cpp: In function 'int solve3(const string&)': main.cpp:44:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 44 | for (int i = 1; i != s.size(); ++ i) { | ~~^~~~~~~~~~~