Crack the Code

#python #fun #codechallenge

With quarantines and lock-downs, most people around the world are stuck and bored in their houses. A lot of fun riddles are circulating in news feeds on social medias. Here's one of those.

Can you crack the code? It's fun to solve by hand but can you crack it using Python? Here's how I did it:

from itertools import product


def first_fifth_condition(candidate, condition):
    common_elements = [digit for digit in candidate if digit in condition]
    return (len(common_elements) == 1) and (
        candidate.index(common_elements[0]) != condition.index(common_elements[0])
    )


def second_condition(candidate):
    condition = (1, 8, 9)
    common_elements = [digit for digit in candidate if digit in condition]
    return (len(common_elements) == 1) and (
        candidate.index(common_elements[0]) == condition.index(common_elements[0])
    )


def third_condition(candidate):
    condition = (9, 6, 4)
    common_elements = [digit for digit in candidate if digit in condition]
    if len(common_elements) != 2:
        return False
    for digit in common_elements:
        if candidate.index(digit) == condition.index(digit):
            return False
    return True


def fourth_condition(candidate):
    condition = (5, 2, 3)
    common_elements = [digit for digit in candidate if digit in condition]
    return len(common_elements) == 0


def find_code():
    # for completeness test all possible permutations with repetition of digits for length 3.
    # We can further optimize by eliminating 0,5,2,3 from the possible candidate calculation.
    for candidate in product(range(10), repeat=3):
        if (
            first_fifth_condition(candidate, (1, 4, 7))
            and second_condition(candidate)
            and third_condition(candidate)
            and fourth_condition(candidate)
            and first_fifth_condition(candidate, (2, 8, 6))
        ):
            return "".join(map(str, candidate))
    return "No solution found."


if __name__ == "__main__":
    print(find_code())