Different methods of counting multiples of k

first-approach.cs

public static long CountDiv1(int a, int b, int k) {
    if (k < 0)
        return CountDiv1(a, b, -k);

    // Adapt this if one of the bounds is exclusive.
    long range = (long) b - (long) a + 1;

    // Get the rough number of elements in the range.
    long number = range / k;

    // We undercounted by one element if the range isn't evenly
    // divisible by k and the remainder covers a value which is.
    // In particular, that value can lie towards either end of the range
    long remainder = range % k;
    if (remainder != 0) {
        bool found = false;
        for (long i = 0; i <= remainder / 2; i += 1)
            if ((a + i) % k == 0 || (b - i) % k == 0)
                found = true;

        if (found)
            number += 1;
    }

    return number;
}

second-approach.cs

public static long CountDiv2(int ia, int b, int k) {
    if (k < 0)
        return CountDiv2(ia, b, -k);

    // Necessary for a = int.MinValue since -int.MinValue overflows.
    long a = ia;

    if (a > 0 && b > 0)
        return b / k - (a - 1) / k;

    if (a < 0 && b < 0)
        return -a / k - (-b - 1) / k;

    // +1 since 0 is also divisible by k.
    return -a / k + b / k + 1;
}