Efficient Algorithm for String Concatenation with Overlap

Question

We need to combine 3 columns in a database by concatenation. However, the 3 columns may contain overlapping parts and the parts should not be duplicated. For example,

<

Answer 1

I'm trying to make this C# as pleasant to read as possible.

    public static string Concatenate(string s1, string s2)
    {
        if (string.IsNullOrEmpty(s1)) return s2;
        if (string.IsNullOrEmpty(s2)) return s1;
        if (s1.Contains(s2)) return s1;
        if (s2.Contains(s1)) return s2;

        char endChar = s1.ToCharArray().Last();
        char startChar = s2.ToCharArray().First();

        int s1FirstIndexOfStartChar = s1.IndexOf(startChar);
        int overlapLength = s1.Length - s1FirstIndexOfStartChar;

        while (overlapLength >= 0 && s1FirstIndexOfStartChar >=0)
        {
            if (CheckOverlap(s1, s2, overlapLength))
            {
                return s1 + s2.Substring(overlapLength);
            }

            s1FirstIndexOfStartChar = 
                s1.IndexOf(startChar, s1FirstIndexOfStartChar);
            overlapLength = s1.Length - s1FirstIndexOfStartChar;

        }

        return s1 + s2;
    }

    private static bool CheckOverlap(string s1, string s2, int overlapLength)
    {
        if (overlapLength <= 0)
            return false;

        if (s1.Substring(s1.Length - overlapLength) == 
            s2.Substring(0, overlapLength))
            return true;

        return false;            
    }

EDIT: I see that this is almost the same as jerryjvl's solution. The only difference is that this will work with the "abcde", "d" case.