| #!/usr/bin/env python | |
| """This script solves the Project Euler problem "Square digit chains". The | |
| problem is: How many starting numbers below ten million will arrive at 89? | |
| """ | |
| def main(): | |
| """Square digit chains""" | |
| # Constants | |
| MAX = 10000000 | |
| count = 0 | |
| cache = { | |
| '1': 1, | |
| '89': 89, | |
| } | |
| for num in range(2, MAX): | |
| chain = [] | |
| final = None | |
| n = ''.join(sorted(digit for digit in str(num))) | |
| while (True): | |
| if n in cache: | |
| final = cache[n] | |
| break | |
| chain.append(n) | |
| n = str(sum(int(digit) * int(digit) for digit in str(n))) | |
| if final == 89: | |
| count += 1 | |
| for n in chain: | |
| cache[n] = final | |
| print(count) | |
| if __name__ == '__main__': | |
| main() | |