Compilare: main.cpp: In function 'int main()': main.cpp:59:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0 ; i < v . size () ; ++ i){ ~~^~~~~~~~~~~~~ main.cpp:64:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 1 ; j < v [i] . size () ; ++ j){ ~~^~~~~~~~~~~~~~~~~ main.cpp:37:21: warning: unused variable 'u' [-Wunused-variable] int k = 0 , u = 0; ^