function Grid(width, height) {
this.width = width;
this.height = height;
this.cells = new Array(width * height);
}
Grid.prototype.valueAt = function(point) {
return this.cells[point.y * this.width + point.x];
};
Grid.prototype.setValueAt = function(point, value) {
this.cells[point.y * this.width + point.x] = value;
};
Grid.prototype.isInside = function(point) {
return point.x >= 0 && point.y >= 0 &&
point.x < this.width && point.y < this.height;
};
Grid.prototype.moveValue = function(from, to) {
this.setValueAt(to, this.valueAt(from));
this.setValueAt(from, undefined);
};