Compilare: user.cpp: In function ‘void buildPre()’: user.cpp:17:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(j < x.size()) { ^ user.cpp: In function ‘int main()’: user.cpp:40:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(j < y.size()) { ^ user.cpp:41:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < x.size() && x[i] == y[j]) { ^ user.cpp:47:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i == x.size()) { ^