technobabble
 
% https://code.google.com/codejam/contest/11254486/dashboard#s=p2
% Problem C. Technobabble
% Round 1B, Problem C, in Picat, by Afa Zhou

import util,mip.

main =>
    T = read_line().to_int(),
    foreach (TC in 1..T)
        N = read_line().to_int(),
        Topics = [Topic : _ in 1..N, Topic = read_line().split()],
        not not dc(TC,N,Topics)                        
    end.

dc(TC,N,Topics) =>
    Map1 = new_map(),
    Map2 = new_map(),
    Bs = new_list(N),
    Bs :: 0..1,
    foreach ({[W1,W2],B} in zip(Topics,Bs))
        regist(W1,B,Map1),
        regist(W2,B,Map2)
    end,
    gen_constr(Map1),
    gen_constr(Map2),
    solve($[min(sum(Bs))],Bs),
    printf(stderr,"Case #%w: %w\n", TC,N-sum(Bs)).

regist(W,B,Map) =>
    Bs = Map.get(W,[]),
    Map.put(W,[B|Bs]).

gen_constr(Map) =>
    foreach ((_ = Bs) in Map)
        sum(Bs) #>= 1
    end.