mc_b.py

def solution(items):
    if not items:
        return

    best = None
    best_count = 0

    current_count = 0
    last = items[0]
    for current in items:
        if current == last:
            current_count += 1
        else:
            current_count = 1
        last = current

        if current == best:
            best_count = current_count
        elif current_count > best_count:
            best = current
            best_count = current_count

    if best_count > len(items) // 2:
        return best


def test_solution():
    assert solution(sorted([])) == None
    assert solution(sorted([1])) == 1
    assert solution(sorted([1, 2])) == None
    assert solution(sorted([1, 2, 3])) == None
    assert solution(sorted([1, 2, 1])) == 1
    assert solution(sorted([1, 2, 1, 2])) == None


if __name__ == "__main__":
    test_solution()