So I Wrote A Backward Version Of KMP Algorithm In C# That Searches String From Right

[Robert Vandenberg Huang]

    public static int LastIndexOf(this IReadOnlyList s, IReadOnlyList t, int startIndex, 
        IEqualityComparer comparer) where T : IEquatable
    {
        Validate(s, t, startIndex);

        // Follow the behavior of string.LastIndexOf(string) method. 
        if (t.Count == 0) return 0;
        if (s.Count == 0 || s.Count < t.Count) return -1;

        if (comparer == null) comparer = EqualityComparer.Default;
        if (t.Count == 1) return LastIndexOf(s, t\[0\], startIndex, comparer);

        var table = BuildTable(t, comparer);
        var i = 0;  

        while (startIndex - i >= 0)  
        {
            if (comparer.Equals(t\[t.Count - i - 1\], s\[startIndex - i\]))
            {
                if (i == t.Count - 1)
                    return startIndex - t.Count + 1;
                i++;
            }
            else
            {
                if (table\[i\] > -1)
                {
                    startIndex -= i;
                    i = table\[i\];
                }
                else
                {
                    startIndex--;
                    i = 0;
                }
            }
        }
        return -1;
    }

Full source code can be seen here[^]. The method works like String.LastIndexOf which searches string from the last character. The BuildTable method is exactly same with normal KMP algorithm. I'm not sure if this is the best solution though.

[Lost User]

I would have just reversed the 2 strings and compared those. (KMP: Keep Me Partying). ;P

"(I) am amazed to see myself here rather than there ... now rather than then". ― Blaise Pascal