Algorithms Difficult questions

[webdev]

1. Bob has n friends: a1,a2,...,an, Bob has also a list L which is a subgroup of {a1,...,an}x{a1,...,an} which specify which of the friends knows each other (i.e. the pair (ai,aj) belongs to L if and only if ai knows aj, ai knows aj if aj knows ai). Bob organize a party and he wants to invite...