.NET (Core and Framework)

Johnkokk wrote:

Does that make any sense ?

Johnkokk wrote:

Do you really think, that the problem is to multiply 2 numbers ?

Johnkokk wrote:

he problem is to find the algorithm ...

int[] factors=new int[factorList.Length];

// This method should return true if number can be factored using some factors from factorList
// we assume factorList items are all different, positive, non-zero, and ordered numerically ascending.

// call this method with minimum=0 and nesting=0; when it returns true read factors array till the product matches.

public bool CanBeFactoredWithSomeOfThese(int number, List<int> factorList, int minimum, int nesting) {
    foreach(int factor in factorList) {
        if (factor<=minimum) continue;
        if (number%factor!=0) continue;
        factors[nesting]=factor;
        bool OK=true;
        if (number>factor) OK=CanBeFactoredWithSomeOfThese(number/factor, largerFactors, factor, nesting+1);
        if (OK) return true;
    }
    return false;
}

public static void TestFactors()
{
    List<string> nodes = GetFactors(160, new int[] { 2, 3, 4, 5, 6, 7, 8, 10, 15, 20, 25, 30, 40, 50, 100, 500 });
    foreach (string n in nodes)
    {
        Console.WriteLine(n);
    }
    Console.ReadKey();
}


private static List<string> GetFactors(int number, int[] possValues)
{
    List<string> nodes = new List<string>();
    for (int j = 0; j < possValues.Count(); j++)
    {
        GetFactorsInner(nodes, number, possValues, j, possValues[j], possValues[j].ToString());

    }
    return nodes;
}

private static void GetFactorsInner(List<string> nodes, int number, int[] possValues, int currIndex, int currTot, string currStr)
{
    for (int i = currIndex + 1; i < possValues.Count(); i++)
    {
        int thisTot = currTot;
        string thisStr = currStr;
        if (thisTot * possValues[i] > number)
        {
            break;
        }
        else if (thisTot * possValues[i] == number)
        {
            thisStr += thisStr == null ? possValues[i].ToString() : ", " + possValues[i].ToString();
            nodes.Add(thisStr);
            break;
        }
        else if (number % (thisTot * possValues[i]) == 0)
        {
            thisStr += thisStr == null ? possValues[i].ToString() : ", " + possValues[i].ToString();
            thisTot *= possValues[i];
            GetFactorsInner(nodes, number, possValues, i, thisTot, thisStr);
        }
    }

}