Task: Strange unique prime triplets




Go: package main

import "fmt"

func isPrime(n int) bool {
    switch {
    case n < 2:
        return false
    case n%2 == 0:
        return n == 2
    case n%3 == 0:
        return n == 3
    default:
        d := 5
        for d*d <= n {
            if n%d == 0 {
                return false
            }
            d += 2
            if n%d == 0 {
                return false
            }
            d += 4
        }
        return true
    }
}

func commatize(n int) string {
    s := fmt.Sprintf("%d", n)
    if n < 0 {
        s = s[1:]
    }
    le := len(s)
    for i := le - 3; i >= 1; i -= 3 {
        s = s[0:i] + "," + s[i:]
    }
    if n >= 0 {
        return s
    }
    return "-" + s
}

func strangePrimes(n int, countOnly bool) int {
    c := 0
    f := "%2d: %2d + %2d + %2d = %2d\n"
    var s int

    for i := 3; i <= n-4; i += 2 {
        if isPrime(i) {
            for j := i + 2; j <= n-2; j += 2 {
                if isPrime(j) {
                    for k := j + 2; k <= n; k += 2 {
                        if isPrime(k) {
                            s = i + j + k
                            if isPrime(s) {
                                c++
                                if !countOnly {
                                    fmt.Printf(f, c, i, j, k, s)
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    return c
}

func main() {
    fmt.Println("Unique prime triples under 30 which sum to a prime:")
    strangePrimes(29, false)
    cs := commatize(strangePrimes(999, true))
    fmt.Printf("\nThere are %s unique prime triples under 1,000 which sum to a prime.\n", cs)
}





VB: Imports DT = System.DateTime

Module Module1

    Iterator Function Primes(lim As Integer) As IEnumerable(Of Integer)
        Dim flags(lim) As Boolean

        Dim j = 2

        Dim d = 3
        Dim sq = 4
        While sq <= lim
            If Not flags(j) Then
                Yield j
                For k = sq To lim Step j
                    flags(k) = True
                Next
            End If

            j += 1
            d += 2
            sq += d
        End While

        While j <= lim
            If Not flags(j) Then
                Yield j
            End If
            j += 1
        End While
    End Function

    Sub Main()
        For Each lmt In {90, 300, 3000, 30000, 111000}
            Dim pr = Primes(lmt).Skip(1).ToList()
            Dim st = DT.Now
            Dim f = 0
            Dim r As New List(Of String)
            Dim i = -1
            Dim m = lmt \ 3
            Dim h = m
            While i < 0
                i = pr.IndexOf(h)
                h -= 1
            End While
            Dim j = i - 1
            Dim k = j - 1
            For a = 0 To k
                Dim pra = pr(a)
                For b = a + 1 To j
                    Dim prab = pra + pr(b)
                    For c = b + 1 To i
                        Dim d = prab + pr(c)
                        If Not pr.Contains(d) Then
                            Continue For
                        End If
                        f += 1
                        If lmt < 100 Then
                            r.Add(String.Format("{3,5} = {0,2} + {1,2} + {2,2}", pra, pr(b), pr(c), d))
                        End If
                    Next
                Next
            Next
            Dim s = "s.u.p.t.s under "
            r.Sort()
            If r.Count > 0 Then
                Console.WriteLine("{0}{1}:" + vbNewLine + "{2}", s, m, String.Join(vbNewLine, r))
            End If
            If lmt > 100 Then
                Console.WriteLine("Count of {0}{1,6:n0}: {2,13:n0}  {3} sec", s, m, f, (DT.Now - st).ToString().Substring(6))
            End If
        Next
    End Sub

End Module