"""
Exercise 2: Hamming Distance (LeetCode 461)

Return the number of bit positions where x and y differ: popcount(x ^ y).
"""

def hamming_distance(x, y):
    # TODO
    return -1


# --- self-check: do not modify below this line ---
a, b, c = hamming_distance(1, 4), hamming_distance(3, 1), hamming_distance(0, 0)
print(a, b, c)
print("PASS" if (a, b, c) == (2, 1, 0) else "FAIL")