Algorithms

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