Compilare: main.cpp: In function 'void solve(std::__cxx11::string&)': main.cpp:36:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < s.size (); i++) { ~~^~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:104:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("abba.in", "r", stdin); ^ main.cpp:105:38: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("abba.out", "w", stdout); ^