System.OutOfMemoryException when generating permutations

Question

I\'m getting System.OutOfMemoryException when trying to generate 6 letter permutations. 5 letter permutations still work.

Here is the code I\'m using to

Answer 1

The best thing to do here is to use the lazy initialization to avoid having all the permutations in memory at the same time.

private static IEnumerable getPermutations(int n,string source)
{
    IEnumerable q = source.Select(x => x.ToString());
    for (int i = 0; i < n - 1; i++)
    {
        q = q.SelectMany(x => source, (x, y) => x + y);
    }

    return q; 
}

private static List filterListByRegex(IEnumerable list, string regex)
{
    List newList = new List();
    foreach(var item in list)
    {
        Match match = Regex.Match(item, regex, RegexOptions.IgnoreCase);
        if (match.Success)
        {
            newList.Add(item);
        }
    }

    return newList;
}

This may not be the most efficient way to do it, but at least it should get you past the memory issues.