Find the first occurrence/starting index of the sub-array in C#

Question

Given two arrays as parameters (x and y) and find the starting index where the first occurrence of y in x. I am wondering what the simplest or the fastest implementation would be.

Example:

when x = {1,2,4,2,3,4,5,6}
     y =       {2,3}
result
     starting index should be 3

Update: Since my code is wrong I removed it from the question.

Answer 1

Simplest to write?

    return (from i in Enumerable.Range(0, 1 + x.Length - y.Length)
            where x.Skip(i).Take(y.Length).SequenceEqual(y)
            select (int?)i).FirstOrDefault().GetValueOrDefault(-1);

Not quite as efficient, of course... a bit more like it:

private static bool IsSubArrayEqual(int[] x, int[] y, int start) {
    for (int i = 0; i < y.Length; i++) {
        if (x[start++] != y[i]) return false;
    }
    return true;
}
public static int StartingIndex(this int[] x, int[] y) {
    int max = 1 + x.Length - y.Length;
    for(int i = 0 ; i < max ; i++) {
        if(IsSubArrayEqual(x,y,i)) return i;
    }
    return -1;
}