Compilare: main.cpp: In function 'void bk(int)': main.cpp:50:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < next_elem[v[k - 1]].size(); ++i) { ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.cpp: In function 'bool valid(int)': main.cpp:47:1: warning: control reaches end of non-void function [-Wreturn-type] } ^