Compilare: main.cpp: In function 'int main()': main.cpp:30:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < a.size()) { ~~^~~~~~~~~~ main.cpp:33:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(j < a.size() && a[i].first == a[j].first) ~~^~~~~~~~~~ main.cpp:37:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(j < a.size()) ~~^~~~~~~~~~ main.cpp:36:11: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses] if(sol > 0) ^