C# Array Subset fetching

Question

I have an array of bytes and i want to determine if the contents of this array of bytes exists within another larger array as a continuous sequence. What is the simplest way to go about doing this?

Answer 1

The naive approach is:

public static bool IsSubsetOf(byte[] set, byte[] subset) {
    for(int i = 0; i < set.Length && i + subset.Length <= set.Length; ++i)
        if (set.Skip(i).Take(subset.Length).SequenceEqual(subset))
            return true;
    return false;
}

For more efficient approaches, you might consider more advanced string matching algorithms like KMP.

Answer 2

Try to adapt some string search algorithm. One of the fastest is Boyer-Moore . It's quite easy as well. For binary data, Knuth-Morris-Pratt algorithm might work very efficiently as well.

Answer 3

This, which is a 1/1 port of this answer: http://stackoverflow.com/questions/1507780/searching-for-a-sequence-of-bytes-in-a-binary-file-with-java

Is a very efficient way of doing so:

public static class KmpSearch {

    public static int IndexOf(byte[] data, byte[] pattern) {
        int[] failure = ComputeFailure(pattern);

        int j = 0;
        if (data.Length == 0) return -1;

        for (int i = 0; i < data.Length; i++) {
            while (j > 0 && pattern[j] != data[i]) {
                j = failure[j - 1];
            }
            if (pattern[j] == data[i]) { j++; }
            if (j == pattern.Length) {
                return i - pattern.Length + 1;
            }
        }
        return -1;
    }


    private static int[] ComputeFailure(byte[] pattern) {
        int[] failure = new int[pattern.Length];

        int j = 0;
        for (int i = 1; i < pattern.Length; i++) {
            while (j > 0 && pattern[j] != pattern[i]) {
                j = failure[j - 1];
            }
            if (pattern[j] == pattern[i]) {
                j++;
            }
            failure[i] = j;
        }

        return failure;
    }
}