Compilare: user.cpp: In function ‘void build()’: user.cpp:38:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=2; i<s.length(); i++) ^ user.cpp: In function ‘int main()’: user.cpp:88:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<sol.size(); i++) ^