advent.p6

multi advent('day07', '2', Str $in) {
  my SetHash %prereqs = parse-prereqs($in);
  my $time = 0;
  my @queue;

  while %prereqs || @queue {
    my @available = %prereqs.grep(!*.value).map(*.key).sort;

    # Assign as many free workers to available tasks as possible.
    while @queue < 5 && @available {
      my $task = @available.shift;
      @queue.push: $task => $time + 60 + ($task.ord - 'A'.ord + 1);
      %prereqs{$task}:delete;
    }

    # Step forward in time and finish a task.
    @queue.=sort(*.value);
    (my $task, $time) = @queue.shift.kv;
    $_{$task}-- for %prereqs.values;
  }

  $time
}