Hi Guys !
Sorry for my late answer as i've been a bit busy these days.

Thank you for all your answers !

@wysota, the problem with this solution is that sometimes you need to insert a label in a particular "position", for exemple list[label] = equiValentLabel, which can generate some errors.
@d_stranz i will try your solution as soon as possible and keep you in touch, it seems that it may work very well !

@yeye_olive, this is exactly what i'm trying to do, a union-find.

Thank you very much guys !