问使用Linq在IEnumerable<T>中查找序列

EN

public static class ExtensionMethods
{
    public static int IndexOfSequence<T>(this IEnumerable<T> source, IEnumerable<T> sequence)
    {
        return source.IndexOfSequence(sequence, EqualityComparer<T>.Default);
    }

    public static int IndexOfSequence<T>(this IEnumerable<T> source, IEnumerable<T> sequence, IEqualityComparer<T> comparer)
    {
        var seq = sequence.ToArray();

        int p = 0; // current position in source sequence
        int i = 0; // current position in searched sequence
        var prospects = new List<int>(); // list of prospective matches
        foreach (var item in source)
        {
            // Remove bad prospective matches
            prospects.RemoveAll(k => !comparer.Equals(item, seq[p - k]));

            // Is it the start of a prospective match ?
            if (comparer.Equals(item, seq[0]))
            {
                prospects.Add(p);
            }

            // Does current character continues partial match ?
            if (comparer.Equals(item, seq[i]))
            {
                i++;
                // Do we have a complete match ?
                if (i == seq.Length)
                {
                    // Bingo !
                    return p - seq.Length + 1;
                }
            }
            else // Mismatch
            {
                // Do we have prospective matches to fall back to ?
                if (prospects.Count > 0)
                {
                    // Yes, use the first one
                    int k = prospects[0];
                    i = p - k + 1;
                }
                else
                {
                    // No, start from beginning of searched sequence
                    i = 0;
                }
            }
            p++;
        }
        // No match
        return -1;
    }
}

public static int ContainsSubsequence<T>(this IEnumerable<T> elements, IEnumerable<T> subSequence) where T: IEquatable<T>
{
    return ContainsSubsequence(elements, 0, subSequence);
}

private static int ContainsSubsequence<T>(IEnumerable<T> elements, int index, IEnumerable<T> subSequence) where T: IEquatable<T>
{
    // Do we have any elements left?
    bool elementsLeft = elements.Any();

    // Do we have any of the sub-sequence left?
    bool sequenceLeft = subSequence.Any();

    // No elements but sub-sequence not fully matched
    if (!elementsLeft && sequenceLeft)
        return -1; // Nope, didn't match

    // No elements of sub-sequence, which means even if there are
    // more elements, we matched the sub-sequence fully
    if (!sequenceLeft)
        return index - subSequence.Count(); // Matched!

    // If we didn't reach a terminal condition,
    // check the first element of the sub-sequence against the first element
    if (subSequence.First().Equals(e.First()))
        // Yes, it matched - move onto the next. Consume (skip) one element in each
        return ContainsSubsequence(elements.Skip(1), index + 1 subSequence.Skip(1));
    else
        // No, it didn't match. Try the next element, without consuming an element
        // from the sub-sequence
        return ContainsSubsequence(elements.Skip(1), index + 1, subSequence);
}