Compilare: user.cpp: In function ‘void construct(int, int, int)’: user.cpp:43:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i1 < a[left].size() && i2 < a[right].size()) { ^ user.cpp:43:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i1 < a[left].size() && i2 < a[right].size()) { ^ user.cpp:51:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( ; i1 < a[left].size() ; ++i1) a[node].push_back(a[left][i1]); ^ user.cpp:52:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( ; i2 < a[right].size(); ++i2) a[node].push_back(a[right][i2]); ^