Triangle puzzle

solver.js

/*
     0
    1 1
   1 1 1
  1 1 1 1
 1 1 1 1 1

     |
     v

     1
    0 0
   0 0 0
  0 0 0 0
 0 0 0 0 0


xx.
xxx
.xx

*/
function countBits (n) {
  n -= (n >> 1) & 0x55555555;
  n = (n & 0x33333333) + ((n >> 2) & 0x33333333);
  return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24;
}

function Field(size) {
  var n = size*(size+1)/2;
  this.size = size;
  this.data = (1 << n) - 1;
  this.set(0, 0, 0);
  this.length = n - 1;
}
Field.prototype = {
  _toBit: function(x, y) {
    if (x < 0) return -1; // throw new RangeError("x should be non-negative");
    if (y < 0) return -1; // throw new RangeError("y should be non-negative");
    if (x >= this.size) return -1; // throw new RangeError("x should be less than size");
    if (y >= this.size) return -1; // throw new RangeError("y should be less than size");
    if (x > y) return -1; // throw new RangeError("position should be within triangle");
    return y*(y+1)/2 + x;
  },
  get: function (x, y) {
    var bit = this._toBit(x, y);
    if (bit === -1) return -1;
    var mask = 1 << bit;
    return +!!(this.data & mask);
  },
  set: function (x, y, v) {
    var mask = 1 << this._toBit(x, y);
    if (v) {
      this.data |= mask;
    } else {
      this.data &= ~mask;
    }
  },
  store: function () {
    return this.data;
  },
  load: function (data) {
    this.data = data;
    this.length = countBits(data);
  },
  check: function (x, y, dx, dy) {
    return (
      this.get(x+dx,   y+dy) === 1 &&
      this.get(x+dx*2, y+dy*2) === 0
    );
  },
  move: function (x, y, dx, dy) {
    this.set(x,      y,      0);
    this.set(x+dx,   y+dy,   0);
    this.set(x+dx*2, y+dy*2, 1);
    this.length--;
    return true;
  },
  tryMove: function (x, y, dx, dy) {
    return this.check.apply(this, arguments) &&
      this.move.apply(this, arguments);
  },
  toString: function () {
    var x, y, i, s, a = [];
    for (y = 0; y < this.size; y++) {
      s = "";
      for (x = this.size; x >= y; x--) s += " ";
      for (x = 0; x <= y; x++) s += this.get(x, y) + " ";
      a.push(s);
    }
    return a.join("\n");
  }
};


var F = new Field(5),
  d = [[-1,0],[-1,-1],[0,-1],[1,0],[1,1],[0,1]];
(function r (field) {
  var x, y, i, moved = false;
  F.load(field);
  if (F.length === 1 && F.get(0, 0) === 1) return true;
  for (y = 0; y < F.size; y++) {
  for (x = 0; x <= y; x++) {
  if (F.get(x, y) !== 1) continue;
  for (i = 0; i < 6; i++) {
    if (!F.tryMove(x, y, d[i][0], d[i][1])) continue;
    moved = true;
    if (r(F.store())) {
      F.load(field);
      console.log(F + '');
      return true;
    }
    F.load(field);
  }}}
  if (!moved) return false; // no more moved;
}(F.store()));