Data update

Task/15-puzzle-solver/Dart/15-puzzle-solver.dart

@@ -0,0 +1,78 @@
+import 'package:collection/collection.dart';
+
+typedef OffsetFunction = int Function(int a, int b);
+Function eq = const ListEquality().equals;
+
+/// Solve Random 15 Puzzles
+class FifteenSolver {
+  static const target = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 0];
+  static const trN = [3, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3];
+  static const tcN = [3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2];
+  var pos0 = List.filled(100, 0);
+  var moves = List.filled(100, 0);
+  var dirs = List.filled(100, '');
+  int step = 0, best = 0;
+  var board = List.generate(100, (int i) => List.filled(16, 0));
+
+  bool isFinished() {
+    if (moves[step] < best) return nextMove();
+    if (eq(board[step], target)) {
+      print("Solution found in $step moves :${dirs.join('')}");
+      return true;
+    }
+    return (moves[step] == best) ? nextMove() : false;
+  }
+
+  var passNumber = 0;
+
+  /// Try all valid moves from here, but don't retrace your steps.
+  /// Return true if a solution is found.
+  bool nextMove() {
+    // if (passNumber++ ~/ 100000 == 0) print("${dirs.join('')}");
+    return (dirs[step] != 'u' && pos0[step] ~/ 4 < 3 && down()) ||
+        (dirs[step] != 'd' && pos0[step] ~/ 4 > 0 && up()) ||
+        (dirs[step] != 'l' && pos0[step] % 4 < 3 && right()) ||
+        (dirs[step] != 'r' && pos0[step] % 4 > 0 && left()) ||
+        false;
+  }
+
+  bool move(int offset, String dir, List<int> rcArray, OffsetFunction rcFunc) {
+    final int ix = pos0[step] + offset;
+    final n = board[step][ix];
+    pos0[step + 1] = pos0[step] + offset;
+    board[step + 1] = board[step].toList()
+      ..[pos0[step]] = n
+      ..[ix] = 0;
+    dirs[step + 1] = dir;
+    moves[step + 1] = moves[step] + rcFunc(rcArray[n], pos0[step]);
+    step++;
+    if (isFinished()) return true;
+    step--;
+    return false;
+  }
+
+  bool right() => move(1, 'r', tcN, (a, b) => (a <= b % 4 ? 0 : 1));
+  bool left() => move(-1, 'l', tcN, (a, b) => (a >= b % 4 ? 0 : 1));
+  bool down() => move(4, 'd', trN, (a, b) => (a <= b ~/ 4 ? 0 : 1));
+  bool up() => move(-4, 'u', trN, (a, b) => (a >= b ~/ 4 ? 0 : 1));
+
+  void solve(List<int> initBoard) {
+    pos0[0] = initBoard.indexOf(0);
+    board[0] = initBoard;
+    while (!isFinished()) best++;
+  }
+}
+
+void main(List<String> args) {
+  print("running");
+  // test values
+  // final start = [5, 1, 2, 3, 6, 10, 7, 4, 13, 9, 11, 8, 14, 0, 15, 12];
+  // final start = [9, 1, 2, 4, 13, 6, 5, 7, 3, 11, 14, 15, 10, 0, 8, 12];
+  // final start = [10, 3, 1, 4, 13, 5, 8, 7, 9, 6, 0, 11, 14, 15, 12, 2];
+  // required solution
+  final start = [15, 14, 1, 6, 9, 11, 4, 12, 0, 10, 7, 3, 13, 8, 5, 2];
+  // Extra credit
+  // final start = [0, 12, 9, 13, 15, 11, 10, 14, 3, 7, 2, 5, 4, 8, 6, 1];
+  print(start);
+  FifteenSolver().solve(start);
+}