Parallel calculations: Difference between revisions

<lang csharp>using System;

using System.Collections.Generic;

using System.Linq;

class Program

{

public static List<int> PrimeFactors(int number)

{

var primes = new List<int>();

for (int div = 2; div <= number; div++)

{

while (number % div == 0)

{

primes.Add(div);

number = number / div;

}

}

return primes;

}

static void Main(string[] args)

{

int[] n = { 12757923, 12878611, 12757923, 15808973, 15780709, 197622519 };

// Calculate each of those numbers' prime factors, in parallel

var factors = n.AsParallel().Select(PrimeFactors).ToList();

// Make a new list showing the smallest factor for each

var smallestFactors = factors.Select(thisNumbersFactors => thisNumbersFactors.Min()).ToList();

// Find the index that corresponds with the largest of those factors

int biggestFactor = smallestFactors.Max();

int whatIndexIsThat = smallestFactors.IndexOf(biggestFactor);

Console.WriteLine("{0} has the largest minimum prime factor: {1}", n[whatIndexIsThat], biggestFactor);

Console.WriteLine(string.Join(" ", factors[whatIndexIsThat]));

}

}</lang>

{{out}}

<pre>12878611 has the largest minimum prime factor: 47

47 101 2713</pre>

Another version, using Parallel.For:

{{out}}