https://brilliant.org/daily-problems/grid-fill-nine-cross/

brilliant_the_nine_nine_plus.py

from more_itertools import set_partitions

S = set(range(1,6))
for i in S:
    s_i = S - {i}
    for left, right in set_partitions(s_i, 2):
        if len(left) == len(right) and sum(left) + i == 9 and sum(right) + i == 9:
            print(i, left, right)
            break