day_25.py

#!/usr/bin/python3


def FindLoopSize(public_key, subject_number):
    count = 0
    value = 1
    while True:
        count = count + 1
        value = value * subject_number
        value = value % 20201227
        if value == public_key:
            break
    return count


def GenerateEncrytionKey(subject_number, loop_size):
    value = 1
    for i in range(0, loop_size):
        value = value * subject_number
        value = value % 20201227
    return value


def main():
    file = open("../input/day_25_input")
    line = file.readline()
    line = line.strip("\n")
    card_public_key = int(line)
    card_subject_number = 7
    card_loop_size = FindLoopSize(card_public_key, card_subject_number)

    line = file.readline()
    line = line.strip("\n")
    door_public_key = int(line)
    door_subject_number = 7
    door_loop_size = FindLoopSize(door_public_key, door_subject_number)

    encryption_key = GenerateEncrytionKey(card_public_key, door_loop_size)
    print(encryption_key)
    return encryption_key


if __name__ == "__main__":
    main()