project-euler/Yet to solve/773 Ruff Numbers -- v2.sf

#!/usr/bin/ruby

# https://projecteuler.net/problem=773

func ruff_generator(k) {
    Enumerator({|f|

        var P = [2,5, k.by { .is_prime && (_%10 == 7) }...]
        var c = P.prod
        var a = []

        say "c = prod(#{P}) = #{c}"

        for n in (1..c) {
            n.is_coprime(c) || next
            if (n % 10 == 7) {
                a.push(n)
                f(n)
            }
        }

        loop {
            var n = (a.shift + c)
            if (n % 10 == 7) {
                a.push(n)
                f(n)
            }
        }
    })
}

# F(3) = 76101452
# F(4) = 164491606552

var k = 3
var c = [2,5, k.by { .is_prime && (_%10 == 7) }...].prod
var r = ruff_generator(k)

say r.while { _ < c }.sum