public int hamming() {
		int compare = 1;
		if (!hammed) {
			for (int i = 0; i < tiles.length; i++) {
				for (int j = 0; j < tiles[i].length; j++) {
					if (tiles[i][j] != 0) {
						if (tiles[i][j] != compare) {
							hamming++;
						}
					}
					compare++;
				}
			}
			hammed = true;
			return hamming;
		}
		return hamming;
	} // number of blocks out of place