6 kyu hard problem (imo 4kyu) https://www.codewars.com/kata/5ef9c85dc41b4e000f9a645f/train/python

Decode-the-QR-Code.py

positions = [
    (20, 18),
    (19, 18),
    (20, 17),
    (19, 17),
    (20, 16),
    (19, 16),
    (20, 15),
    (19, 15),
    (20, 14),
    (19, 14),
    (20, 13),
    (19, 13),
    (20, 12),
    (19, 12),
    (20, 11),
    (19, 11),
    (20, 10),
    (19, 10),
    (20, 9),
    (19, 9),
    (18, 9),
    (17, 9),
    (18, 10),
    (17, 10),
    (18, 11),
    (17, 11),
    (18, 12),
    (17, 12),
    (18, 13),
    (17, 13),
    (18, 14),
    (17, 14),
    (18, 15),
    (17, 15),
    (18, 16),
    (17, 16),
    (18, 17),
    (17, 17),
    (18, 18),
    (17, 18),
    (18, 19),
    (17, 19),
    (18, 20),
    (17, 20),
    (16, 20),
    (15, 20),
    (16, 19),
    (15, 19),
    (16, 18),
    (15, 18),
    (16, 17),
    (15, 17),
    (16, 16),
    (15, 16),
    (16, 15),
    (15, 15),
    (16, 14),
    (15, 14),
    (16, 13),
    (15, 13),
    (16, 12),
    (15, 12),
    (16, 11),
    (15, 11),
    (16, 10),
    (15, 10),
    (16, 9),
    (15, 9),
    (14, 9),
    (13, 9),
    (14, 10),
    (13, 10),
]


def scanner(qrcode):
    bits = "".join(
        map(lambda pos: str(unmask(qrcode[pos[1]][pos[0]], pos[0], pos[1])), positions)
    )

    length = int(bits[0:8], 2)
    chars = [
        chr(int(bits[8:16], 2)),
        chr(int(bits[16:24], 2)),
        chr(int(bits[24:32], 2)),
        chr(int(bits[32:40], 2)),
        chr(int(bits[40:48], 2)),
        chr(int(bits[48:56], 2)),
        chr(int(bits[56:64], 2)),
        chr(int(bits[64:72], 2)),
    ]

    print(length)
    print(chars)

    return "".join(chars[0:length])


def unmask(bit, x, y):
    return invert(bit) if ((x + y) % 2) == 0 else bit


def invert(bit):
    return 0 if bit == 1 else 1


"""    
[ 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1 ]
[ 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1 ]
[ 1, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1 ]
[ 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1 ]
[ 1, 0, 1, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1 ]
[ 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1 ]
[ 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1 ]
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 ]
[ 0, 0, 1, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1 ]
[ 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1 ]
[ 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1 ]
[ 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0 ]
[ 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0 ]
[ 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0 ]
[ 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 1 ]
[ 1, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0 ]
[ 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 0, 1, 0, 0, 0, 1, 1 ]
[ 1, 0, 1, 1, 1, 0, 1, 0, 0, 0, 1, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0 ]
[ 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 0, 1, 1, 0, 1, 0, 1, 0, 1 ]
[ 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0 ]
[ 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 0, 0, 1, 1 ]
"""