Compilare: user.cpp: In function ‘void solve(int)’: user.cpp:14:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (solution.size() == k) { ~~~~~~~~~~~~~~~~^~~~ user.cpp: In function ‘int main()’: user.cpp:30:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("combinari.in", "r", stdin); ^ user.cpp:31:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("combinari.out", "w", stdout); ^ user.cpp:33:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &n, &k); ^