Compilare: main.cpp: In function 'int main()': main.cpp:18:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < v.size(); ++i) { ~~^~~~~~~~~~ main.cpp:21:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i == v.size() - 1 || v[i + 1].first != v[i].first) ~~^~~~~~~~~~~~~~~