help,my c# solution only has 19/23 test failed .Does it has anything to do with using List?

public static int anotherMinimaxProblem(List a) { int max = int.MaxValue; for (int i = 0; i < a.Count; i++) {

    int maxima = 0;
    for (int j = 0; j < a.Count; j++)
    {
        if (i == j)
        {
            continue;
        }
        int answer = a[i] ^ a[j];
        if (answer > maxima)
        {
            maxima = answer;
        }
    }
    if (maxima < max)
    {
        max = maxima;
    }
}
return max;

}