gang_warfare.mzn

int: n = 4;                 % number of gangs
set of int: Gang = 1..n;
array[Gang] of int: m = [3, 2, 2, 3];  % size of each gang
int: t = sum(m);
set of int: Time = 1..t;
set of int: Student = 1..t;

%%%%%%%

array[Student] of var Time: interview;    % at what time do we see a given student?

% Which gang is each student in?
array[Student] of Gang: gang = [ g | g in Gang, j in 1..m[g] ];
function array[int] of Student: members(Gang: g) = [ s | s in Student where gang[s] = g ];

% Who is the leader of each gang?
function Student: leader(Gang: g) = min(members(g));

% Confession points for each gang.
array[Gang] of var int: points;

% Does a leader crack?  Yes if there's any other gang whose interviews are already complete.
function var bool: leader_cracks(Gang: g) =
    exists (g2 in Gang) ((max (i in members(g2)) (interview[i])) > interview[leader(g)]);

% Give points for interviewing a leader if he cracks, else don't.
constraint forall (g in Gang)
    (points[g] = if leader_cracks(g)
                 then
                   let { var int: sold_out = sum (i in members(g))
                                             (bool2int(interview[i] > interview[leader(g)])) }
                   in sold_out
                 else 0 endif);

%%%%%%%

solve satisfy;