Deleting a string from another string c#

Question

I want to subtract an inputted string from another inputted string, however the operator "-" is not allowed with strings. Example

s1 = "abcdhello";
s2 = "hellothere";
//i want s3 to be like:
s3 = "abcd";

How can i achieve this, i tried .substring, but it didn't work out.

Update: Let's say i have a key and text, let's consider s1 as a combinedkey, and s2 as the text, i want to get the uncombinedkey.

Answer 1

loop through s1 and s2 finding the longest overlap and returning the difference, or the original value

public static string GetWeird(string s1, string s2)
{
    Console.WriteLine(s1);
    for (int i = Math.Max(0, s1.Length - s2.Length); i < s1.Length; i++)
    {
        var ss1 = s1.Substring(i, s1.Length - i);
        var ss2 = s2.Substring(0, Math.Min(s2.Length, ss1.Length));
        Console.WriteLine(ss2.PadLeft(s1.Length));
        if (ss1 == ss2)
            return s1.Substring(0, i);
    }

    return s1;
}

public static void Main()
{
    var s1 = "5675675756756abcdhello";
    var s2 = "hellothere";
    var s3 = GetWeird(s1, s2);
    Console.WriteLine(s3);
}

Output

5675675756756abcdhello
            hellothere
             hellother
              hellothe
               helloth
                hellot
                 hello
5675675756756abcd

Full Demo Here

Answer 2

Convert both strings to lists of chars and remove chars in the first list if they are in the second.

As simple as that

string s1 = "abcdefg";
string s2 = "efghijk";

List<char> s1l = s1.ToList();
List<char> s2l = s2.ToList();

s1l.RemoveAll(c => s2l.ToList().Exists(n => n == c));

string s3 = String.Concat(s1l);