Question

I’m trying to find multiple ways to solve Project Euler’s problem #13. I’ve already got it solved two different ways, but what I am trying to do this time is to have my solution read from a text file that contains all of the numbers, from there it converts it and adds the column numbers farthest to the right. I also want to solve this problem in a way such that if we were to add new numbers to our list, the list can contain any amount of rows or columns, so it’s length is not predefined (non array? I’m not sure if a jagged array would apply properly here since it can’t be predefined).

So far I’ve got:

    static void Main(string[] args)
    {

        List<int> sum = new List<int>();

        string bigIntFile = @"C:\Users\Justin\Desktop\BigNumbers.txt";

        
        string result;
    
        StreamReader streamReader = new StreamReader(bigIntFile);

        while ((result = streamReader.ReadLine()) != null)
        {
            for (int i = 0; i < result.Length; i++)
            {
                int converted = Convert.ToInt32(result.Substring(i, 1));
                sum.Add(converted);
            }
        }

    }

which reads the file and converts each character from the string to a single int. I’m trying to think how I can store that int in a collection that is like 2D array, but the collection needs to be versatile and store any # of rows / columns. Any ideas on how to store these digits other than just a basic list? Is there maybe a way I can set up a list so it’s like a 2D array that is not predefined? Thanks in advance!

UPDATE: Also I don’t want to use "BigInteger". That’d be a little too easy to read the line, convert the string to a BigInt, store it in a BigInt list and then sum up all the integers from there.

Answer 1

There is no resizable 2D collection built into the .NET framework. I’d just go with the “jagged arrays” type of data structure, just with lists:

List<List<int>>

You can also vary this pattern by using an array for each row:

List<int[]>

If you want to read the file a little simpler, here is how:

List<int[]> numbers =
 File.EnumerateLines(path)
 .Select(lineStr => lineStr.Select(@char => @char - '0').ToArray())
 .ToList();

Far less code. You can reuse a lot of built-in stuff to do basic data transformations. That gives you less code to write and to maintain. It is more extensible and it is less prone to bugs.

If you want to select a column from this structure, do it like this:

int colIndex = ...;
int[] column = numbers.Select(row => row[index]).ToArray();

You can encapsulate this line into a helper method to remove noise from your main addition algorithm.

Note, that the efficiency of all those patterns is far less than a 2D array, but in your case it is good enough.