073 Counting fractions in a range.sf

#!/usr/bin/ruby

# Author: Trizen
# Date: 21 March 2023
# https://github.com/trizen

# https://projecteuler.net/problem=73

# Runtime: 31.865s

func count_frac(max_d, min, max) {
    (min+max .. max_d) -> sum {|n|
        RangeNum(idiv(n,min)+1, idiv(n-1, max)).count_by {|k| n.is_coprime(k) }
    }
}

assert_eq(count_frac(8, 3, 2), 3)

say count_frac(12_000, 3, 2)