upRightFrontToDownLeftFront method

Cube upRightFrontToDownLeftFront(int index)

Implementation

Cube upRightFrontToDownLeftFront(int index) {
  final cp = List.filled(Corner.count, Corner.downRightBottom);
  final corner = [
    Corner.upRightFront, Corner.upFrontLeft, //
    Corner.upLeftBottom, Corner.upBottomRight, //
    Corner.downFrontRight, Corner.downLeftFront, //
  ];
  final otherCorner = [
    Corner.downBottomLeft,
    Corner.downRightBottom,
  ];

  var b = index % 720; // Permutation
  var a = index ~/ 720; // Combination

  // generate permutation from index b
  for (var j = 1; j < 6; j++) {
    var k = b % (j + 1);
    b ~/= j + 1;

    while (k-- > 0) {
      _rotateRight(corner, 0, j);
    }
  }

  var x = 5;

  // generate combination and set edges
  for (var j = Corner.downRightBottom.index; j >= 0; j--) {
    if (a - _cnk(j, x + 1) >= 0) {
      cp[j] = corner[x];
      a -= _cnk(j, x-- + 1);
    }
  }

  x = 0;

  for (var j = Corner.upRightFront.index; j <= Corner.downRightBottom.index; j++) {
    if (cp[j] == Corner.downRightBottom) {
      cp[j] = otherCorner[x++];
    }
  }

  return Cube._(cp: cp, co: _co, ep: _ep, eo: _eo);
}