Counting trailing zeros of numbers resulted from factorial

Question

I\'m trying to count trailing zeros of numbers that are resulted from factorials (meaning that the numbers get quite large). Following code takes a number, compute the facto

Answer 1

My 2 cents: avoid to work with double since they are error-prone. A better datatype in this case is BigInteger, and here there is a small method that will help you:

public class CountTrailingZeroes {

    public int countTrailingZeroes(double number) {
        return countTrailingZeroes(String.format("%.0f", number));
    }

    public int countTrailingZeroes(String number) {
        int c = 0;
        int i = number.length() - 1;

        while (number.charAt(i) == '0') {
            i--;
            c++;
        }

        return c;

    }

    @Test
    public void $128() {
        assertEquals(0, countTrailingZeroes("128"));
    }

    @Test
    public void $120() {
        assertEquals(1, countTrailingZeroes("120"));
    }

    @Test
    public void $1200() {
        assertEquals(2, countTrailingZeroes("1200"));
    }

    @Test
    public void $12000() {
        assertEquals(3, countTrailingZeroes("12000"));
    }

    @Test
    public void $120000() {
        assertEquals(4, countTrailingZeroes("120000"));
    }

    @Test
    public void $102350000() {
        assertEquals(4, countTrailingZeroes("102350000"));
    }

    @Test
    public void $1023500000() {
        assertEquals(5, countTrailingZeroes(1023500000.0));
    }
}