project-euler/Sidef/050 Consecutive prime sum -- v2.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# Date: 25 July 2021
# https://github.com/trizen

# Which prime, below one-million, can be written as the sum of the most consecutive primes?

# https://projecteuler.net/problem=50

# Runtime: 0.227s

func p50 (limit) {

    var prime_sum = [0]

    for (var p = 2; true ; p.next_prime!) {
        var sum = (prime_sum.tail + p)
        break if (sum >= limit)
        prime_sum << sum
    }

    var terms         = 1
    var max_prime     = 2
    var start_p_index = 1

    for i in (^prime_sum) {
        for (var j = prime_sum.end; j >= (i + terms); --j) {

            var n = (prime_sum[j] - prime_sum[i])

            if (((j-i > terms) or (n > max_prime)) and (n < limit) and n.is_prime) {
                (terms, max_prime, start_p_index) = (j-i, n, i+1)
                break
            }
        }
    }

    say "#{max_prime} is the sum of #{terms} consecutive primes with first prime = #{prime(start_p_index)}"
}

p50(1e6)