Pollard's Rho Heuristic
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Pollard's rho heuristic is a method used to find a number's factors. This is faster than the classic brute-force, try every number until sqrt(n) method, but it's results are highly unpredictable. This just prints the factors.
import sys import random def Euclid(a, b): while b != 0: r = a % b a = b b = r return a def PollardRho(n): i = 1 x = random.randint(0, n - 1) y = x k = 2 tried = set() tried.add(x) while True: i = i + 1 x = (x ** 2 - 1) % n if x in tried: return tried.add(x) d = Euclid(y - x, n) if d != 1 and d != n: print d # d is a factor. Print it. if i == k: y = x k = 2 * k def main(argv): PollardRho(int(argv)) if __name__ == "__main__": main(sys.argv[1:])