""" https://projecteuler.net/problem=51 Prime digit replacements Problem 51 By replacing the 1st digit of the 2-digit number *3, it turns out that six of the nine possible values: 13, 23, 43, 53, 73, and 83, are all prime. By replacing the 3rd and 4th digits of 56**3 with the same digit, this 5-digit number is the first example having seven primes among the ten generated numbers, yielding the family: 56003, 56113, 56333, 56443, 56663, 56773, and 56993. Consequently 56003, being the first member of this family, is the smallest prime with this property. Find the smallest prime which, by replacing part of the number (not necessarily adjacent digits) with the same digit, is part of an eight prime value family. """ from collections import Counter from typing import List def prime_sieve(n: int) -> List[int]: """ Sieve of Erotosthenes Function to return all the prime numbers up to a certain number https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes >>> prime_sieve(3) [2] >>> prime_sieve(50) [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47] """ is_prime = [True] * n is_prime[0] = False is_prime[1] = False is_prime[2] = True for i in range(3, int(n ** 0.5 + 1), 2): index = i * 2 while index < n: is_prime[index] = False index = index + i primes = [2] for i in range(3, n, 2): if is_prime[i]: primes.append(i) return primes def digit_replacements(number: int) -> List[List[int]]: """ Returns all the possible families of digit replacements in a number which contains at least one repeating digit >>> digit_replacements(544) [[500, 511, 522, 533, 544, 555, 566, 577, 588, 599]] >>> digit_replacements(3112) [[3002, 3112, 3222, 3332, 3442, 3552, 3662, 3772, 3882, 3992]] """ number = str(number) replacements = [] digits = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"] for duplicate in Counter(number) - Counter(set(number)): family = [int(number.replace(duplicate, digit)) for digit in digits] replacements.append(family) return replacements def solution(family_length: int = 8) -> int: """ Returns the solution of the problem >>> solution(2) 229399 >>> solution(3) 221311 """ numbers_checked = set() # Filter primes with less than 3 replaceable digits primes = { x for x in set(prime_sieve(1_000_000)) if len(str(x)) - len(set(str(x))) >= 3 } for prime in primes: if prime in numbers_checked: continue replacements = digit_replacements(prime) for family in replacements: numbers_checked.update(family) primes_in_family = primes.intersection(family) if len(primes_in_family) != family_length: continue return min(primes_in_family) if __name__ == "__main__": print(solution())