Compilare: main.cpp: In function 'void bt()': main.cpp:42:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(sol.size()==k-1){ ~~~~~~~~~~^~~~~ main.cpp: In function 'int main()': main.cpp:66:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("immortal.in","r",stdin); ^ main.cpp:67:39: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("immortal.out","w",stdout); ^