scoring an n-queens board

n_queens.py

def n_queens_attacks(board_state: str) -> int:
    max_attack_num = 28
    attacks = 0

    # count horizontal attacks
    c = Counter(board_state)
    overlap = {k: v for k, v in c.items() if v > 1}

    for k, v in overlap.items():
        v_prime = v - 1
        num_attacks = v_prime * (v / 2)
        attacks += num_attacks

    # count diagonal attacks
    for i, s in enumerate(board_state):
        for j in range(i+1, 8):
            col_offset = abs(i - j)
            row_offset = abs(int(s) - int(board_state[j]))

            # if x cols over & x rows offset - it is a diagonal attack
            if col_offset == row_offset:
                attacks += 1
                
    return max_attack_num - attacks