project-euler/Sidef/010 Summation of primes -- v2.sf

#!/usr/bin/ruby

# The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.
# Find the sum of all the primes below two million.

# https://projecteuler.net/problem=10

# Runtime: 1.138s

func sum_of_primes(n) {

    return 0 if (n <= 1)

    var r = n.isqrt
    var V = (1..r -> map {|k| idiv(n,k) })
    V << range(V.last-1, 1, -1).to_a...

    var S = Hash(V.map{|k| (k, faulhaber(k,1)) }...)

    for p in (2..r) {
        S{p} > S{p-1} || next
        var sp = S{p-1}
        var p2 = p*p
        V.each {|v|
            break if (v < p2)
            S{v} -= p*(S{idiv(v,p)} - sp)
        }
    }

    return S{n}-1
}

say sum_of_primes(2e6)