Faster algorithm to find unique element between two arrays?

Question

EDIT: For anyone new to this question, I have posted an answer clarifying what was going on. The accepted answer is the one I feel best answers my question

Answer 1

This is a little bit faster:

public static int getUniqueElement(int[] a, int[] b) {
    int ret = 0;
    int i;
    for (i = 0; i < a.length; i++) {
        ret += (a[i] - b[i]);
    }
    return Math.abs(ret - b[i]);
}

It's O(m), but the order doesn't tell the whole story. The loop part of the "official" solution has about 3 * m + 3 * n operations, and the slightly faster solution has 4 * m.

(Counting the loop "i++" and "i < a.length" as one operation each).

-Al.