maxDifference

static int maxDifference(int[] a)
{
    int high = a[0];
    int low = a[0];
    int diff = -1;

    for (int i = 1; i < a.Length; i++)
    {
        int current = a[i];

        if (current > high)
        {
            high = current;
            diff = high - low;
            continue;
        }

        if (current < low)
        {
            low = current;
            high = diff > 0 ? low + diff : low;
        }
    }

    return diff;
}