public static long count(int n, int m) {
		if (0 == m || n == m) {
			return 1;
		}
		return (n > m) ? NumberUtil.factorial(n, n - m) / NumberUtil.factorial(m) : 0;
	}
@Test
	public void countTest() {
		long result = Combination.count(5, 2);
		assertEquals(10, result);

		result = Combination.count(5, 5);
		assertEquals(1, result);

		result = Combination.count(5, 0);
		assertEquals(1, result);

		long resultAll = Combination.countAll(5);
		assertEquals(31, resultAll);
	}