Compare chars in two strings of different length in C#

Question

In C#, Im trying to compare two strings and find out how many chars are different.

I Tried this:

static void Main(String[] args)
{
    var strOne = "abcd";
    var strTwo = "bcd";

    var arrayOne = strOne.ToCharArray();
    var arrayTwo = strTwo.ToCharArray();

    var differentChars = arrayOne.Except(arrayTwo);

    foreach (var character in differentChars)
        Console.WriteLine(character);  //Will print a
}

but there are problems with this:

1. if the strings contain same chars but on different positions within the string
2. it removes the duplicate occurences

If the strings would be the same length I would compare the chars one by one but if one is bigger than the other the positions are different

Answer 1

How about this? Append two strings into one and group them, you will have the count of the chars, > 1 will give the repeatings and = 0 will give the unique ones.

var strOne = "abcd";
var strTwo = "bcd";

var arrayOne = strOne.Concat(strTwo).GroupBy(x => x).Select(x => new { Key = x.Key, Count = x.Count() });

foreach (var character in arrayOne) {
    if (character.Count > 1)
    {
        Console.WriteLine(character.Key); // the repeating chars
    }
}

If the same character appears twice in the same string,

 var strOne = "abbcdd";
 var strTwo = "cd";

 var arrayTwo = strOne.Select(x => new { Key = x, IsExists = strTwo.Any(y => y == x) });

 foreach (var character in arrayTwo) {
     if (character.IsExists)
     {
        Console.WriteLine(character.Key);
     }
 }

Answer 2

You may want to have a look at the Leventshtein Distance Algorithm .

As the article says

the Levenshtein distance between two words is the minimum number of single-character edits (insertions, deletions or substitutions) required to change one word into the other

You can find many reference implementations in the internet, like here or here .

public static int LevenshteinDistance(string s, string t)
    {
        int n = s.Length;
        int m = t.Length;
        int[,] d = new int[n + 1, m + 1];

        if (n == 0)
        {
            return m;
        }

        if (m == 0)
        {
            return n;
        }

        for (int i = 0; i <= n; d[i, 0] = i++)
        {
        }

        for (int j = 0; j <= m; d[0, j] = j++)
        {
        }

        for (int i = 1; i <= n; i++)
        {
            for (int j = 1; j <= m; j++)
            {
                int cost = (t[j - 1] == s[i - 1]) ? 0 : 1;

                d[i, j] = Math.Min(
                    Math.Min(d[i - 1, j] + 1, d[i, j - 1] + 1),
                    d[i - 1, j - 1] + cost);
            }
        }
        return d[n, m];
    }
}