AI homework #3

cannibals-missionaries.dart

/*
  Ali Ghanbari - 970216657
  online compiler: https://dartpad.dev/a2c7d1d325c61bf06df68c85235d8ae9?null_safety=true
*/

const n = 3;
enum Position { Left, Right }
enum Move { MM, M, MC, C, CC, None }

void main() {
  var startingState = new State(3, 3, Position.Right);

  print('M-Left\tC-Left\tBoat\tM-Right\tC-Right');
  print(startingState.row);
  final goal = recursiveDLS(startingState, 12);
  print(goal?.row);
  print('');
  print(goal?.steps.map((e) => e.toString() + '\n').toList());
}

State? recursiveDLS(State state, [int limit = 20]) {
  if (goal(state)) return state;
  if (limit == 0) return null;
  return state.successors
      .where(valid)
      .map((successor) => recursiveDLS(successor, limit - 1))
      .firstWhere(goal, orElse: () => null);
}

class Step {
  final Move move;
  final Position position;

  const Step(this.move, this.position);

  @override
  String toString() => '($move, $position)';
}

// start right
// end left
class State {
  final int missionariesRight;
  final int cannibalsRight;
  final Position boat;
  final List<Step> steps;

  State(
    this.missionariesRight,
    this.cannibalsRight,
    this.boat, [
    Move move = Move.None,
    List<Step> parentSteps = const [],
  ]) : steps = [...parentSteps, Step(move, boat)];

  int get missionariesLeft => n - missionariesRight;

  int get cannibalsLeft => n - cannibalsRight;

  Iterable<State> get successors sync* {
    if (boat == Position.Left) {
      yield State(missionariesRight + 2, cannibalsRight, Position.Right,
          Move.MM, steps);
      yield State(
          missionariesRight + 1, cannibalsRight, Position.Right, Move.M, steps);
      yield State(missionariesRight + 1, cannibalsRight + 1, Position.Right,
          Move.MC, steps);
      yield State(
          missionariesRight, cannibalsRight + 1, Position.Right, Move.C, steps);
      yield State(missionariesRight, cannibalsRight + 2, Position.Right,
          Move.CC, steps);
    } else {
      yield State(
          missionariesRight - 2, cannibalsRight, Position.Left, Move.MM, steps);
      yield State(
          missionariesRight - 1, cannibalsRight, Position.Left, Move.M, steps);
      yield State(missionariesRight - 1, cannibalsRight - 1, Position.Left,
          Move.MC, steps);
      yield State(
          missionariesRight, cannibalsRight - 1, Position.Left, Move.C, steps);
      yield State(
          missionariesRight, cannibalsRight - 2, Position.Left, Move.CC, steps);
    }
  }

  @override
  String toString() {
    return "($missionariesRight, $cannibalsRight, $boat)";
  }

  String get row =>
      '$missionariesLeft\t$cannibalsLeft\t${boat.index == 0 ? 'Left' : 'Right'}\t$missionariesRight\t$cannibalsRight';
}

bool goal(State? s) =>
    s != null ? s.missionariesRight == 0 && s.cannibalsRight == 0 : false;

bool valid(State s) =>
    s.missionariesRight >= 0 &&
    s.cannibalsRight >= 0 &&
    s.missionariesRight <= n &&
    s.cannibalsRight <= n &&
    (s.missionariesRight == 0 || s.missionariesRight >= s.cannibalsRight) &&
    (s.missionariesLeft == 0 || s.missionariesLeft >= s.cannibalsLeft);