Question

Basically, my program will try to generate the list of all possible lowercase 5-letter words. Including all combinations that clearly are not real words like jshcc or mmdzq.

I do that by stacking up a massive amount of calls for a function, which does the word work.

But that’s simply too much, and I get a stack overflow error.

How would someone control that?

Answer 1

Basically, convert from recursion to iteration. Typically that involves creating a Stack<T> as a “logical” stack, or something similar.

However, I’d have expected a method generating a list of all possible 5-letter words to only have a stack about 5 deep – one for each letter. Each stack level would be responsible for one level of letter – so the “top” of the stack would iterate through each possible last letter; the next stack frame down would iterate through every possible fourth letter, calling the method recursively to iterate through all possible last letters etc. Something like this (C# code, but hopefully you can understand it and apply it to VB):

const string Letters = "abcdefghijklmnopqrstuvwxyz";

public static List<string> GenerateValidWords(int length)
{
    List<string> words = new List<string>();
    GenerateValidWords(0, new char[length], words);
    return words;
}

private static void GenerateValidWords(int depth, char[] current,
                                       List<string> words)
{
    foreach (char letter in letters)
    {
        current[depth] = letter;
        if (depth == current.Length - 1)
        {
            string word = new string(current);
            if (IsValid(word))
            {
                words.Add(word);
            }
        }
        else
        {
            GenerateValidWords(depth + 1, current, words);
        }
    }
}

Now if you don’t have any sort of filtering, that’s going to generate 11,881,376 words – which at 24 bytes each (on x86) is about 285MB – plus all the space for the list etc. That shouldn’t kill a suitably big machine, but it is quite a lot of memory. Are you sure you need all of these?