Detect differences between two strings

Question

I have 2 strings

string a = \"foo bar\";
string b = \"bar foo\";

and I want to detect the changes from a to b. <

Answer 1

Here might be another solution, full code and commented. However the result of your first original example is inverted :

class Program
{
    enum CharState
    {
        Add,
        Equal,
        Remove
    }

    struct CharResult
    {
        public char c;
        public CharState state;
    }

    static void Main(string[] args)
    {
        string a = "asdfghjk";
        string b = "wsedrftr";
        while (true)
        {
            Console.WriteLine("Enter string a (enter to quit) :");
            a = Console.ReadLine();
            if (a == string.Empty)
                break;
            Console.WriteLine("Enter string b :");
            b = Console.ReadLine();

            List result = calculate(a, b);
            DisplayResults(result);
        }
        Console.WriteLine("Press a key to exit");
        Console.ReadLine();
    }

    static List calculate(string a, string b)
    {
        List res = new List();
        int i = 0, j = 0;

        char[] array_a = a.ToCharArray();
        char[] array_b = b.ToCharArray();

        while (i < array_a.Length && j < array_b.Length)
        {
            //For the current char in a, we check for the equal in b
            int index = b.IndexOf(array_a[i], j);
            if (index < 0) //not found, this char should be removed
            {
                res.Add(new CharResult() { c = array_a[i], state = CharState.Remove });
                i++;
            }
            else
            {
                //we add all the chars between B's current index and the index
                while (j < index)
                {
                    res.Add(new CharResult() { c = array_b[j], state = CharState.Add });
                    j++;
                }
                //then we say the current is the same
                res.Add(new CharResult() { c = array_a[i], state = CharState.Equal });
                i++;
                j++;
            }
        }

        while (i < array_a.Length)
        {
            //b is now empty, we remove the remains
            res.Add(new CharResult() { c = array_a[i], state = CharState.Remove });
            i++;
        }
        while (j < array_b.Length)
        {
            //a has been treated, we add the remains
            res.Add(new CharResult() { c = array_b[j], state = CharState.Add });
            j++;
        }

        return res;
    }

    static void DisplayResults(List results)
    {
        foreach (CharResult r in results)
        {
            Console.WriteLine($"'{r.c}' - {r.state}");
        }
    }
}