def nearestGreater(a):
    b = [-1] * len(a)

    # create sorted pairs of indices and values; since sort is stable
    # it allows to simplify choosing the correct item.
    pairs = sorted(enumerate(a), key=lambda pair: pair[1])

    for i, pair in enumerate(pairs):
        neighbor = min(
            pairs[i + 1:],
            key=lambda p: abs(p[0] - pair[0]) if p[1] != pair[1] else pairs[-1][0],
            default=None)
        if neighbor:
            b[pair[0]] = neighbor[0]

    return b