public static void main(String[] args) {
		HashSet<Integer> pandigital = new HashSet<Integer>();
		// Test multiplication of 1 digit x 4 digit number
		for (int i = 1; i < 10; i++)
			for (int j = 1000; j < 10000; j++) {
				int product = i * j;
				if (isPandigital(concatenate(i, j, product)))
					pandigital.add(product);
			}
		// Test multiplication of 2 digit x 3 digit number
		for (int i = 10; i < 101; i++)
			for (int j = 100; j < 1000; j++) {
				int product = i * j;
				if (isPandigital(concatenate(i, j, product)))
					pandigital.add(product);
			}
		int sum = 0;
		for (int product : pandigital)
			sum += product;
		System.out.println(sum);
		// Solution: 45228
	}