Compilare: user.cpp: In function ‘void solve()’: user.cpp:28:47: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(!S.empty() && size-i > M-S.size() && S.top() < buf[i]) ^ user.cpp:34:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(S.size() < M) ^ user.cpp:23:10: warning: variable ‘x’ set but not used [-Wunused-but-set-variable] char x; ^