get common prefix of two string

Question

I am trying to compare two string in C# but I cant find a way to get the result I need without building something myself.

The strings:

TestasdOne
TestasdTwo

The result:

Testasd

I tried linq but could not get it to work. I tried Google.

Thanks in advance.

Answer 1

Here is the non-linq version which is more efficient, clear and readable

public static string CommonPrefix(string a, string b)
{
    if (a == null)
        throw new ArgumentNullException(nameof(a));

    if (b == null)
        throw new ArgumentNullException(nameof(b));

    var min = Math.Min(a.Length, b.Length);
    var sb = new StringBuilder(min);
    for (int i = 0; i < min && a[i] == b[i]; i++)
        sb.Append(a[i]);

    return sb.ToString();
}

use it like

Console.WriteLine(CommonPrefix("TestasdOne", "TestasdTwo")); //Testasd

Answer 2

Using linq you can do this.

string str1 = "TestasdOne";
string str2 = "TestasdTwo";

string similar = string.Join("", str1.TakeWhile((ch, i) => i < str2.Length && str2[i] == ch));

This will take the characters of first string while its characters are equal to characters of second string at same index.