Project Euler #60
3 Gennaio 2013
The primes 3, 7, 109, and 673, are quite remarkable. By taking any two primes and concatenating them in any order the result will always be prime. For example, taking 7 and 109, both 7109 and 1097 are prime. The sum of these four primes, 792, represents the lowest sum for a set of four primes with this property. Find the lowest sum for a set of five primes for which any two primes concatenate to produce another prime.
python:
import time import itertools as it ts = time.time() def is_prime(num): if num <= 1: return False elif num == 2: return True elif num % 2 == 0: return False else: d = 3 r = int(num**0.5) while d <= r: if num % d == 0: return False d += 2 return True def conc_primes(n, m): return is_prime(int(str(n) + str(m))) and is_prime(int(str(m) + str(n))) def prime_pairs(iterable): for n, m in it.combinations(iterable, 2): if not conc_primes(n, m): return False return True primes = [n for n in xrange(3,10000,2) if is_prime(n)] + [2] def get_five(): for n in primes: for m in primes[primes.index(n):]: if conc_primes(n ,m): for x in primes[primes.index(m):]: if prime_pairs([x, n, m]): for y in primes[primes.index(x):]: if prime_pairs([y, x, n, m]): for z in primes[primes.index(y):]: if prime_pairs([z, y, x, n, m]): return sum([z, y, x, n, m]) res = get_five() print "euler 60: {}\nelapsed time: {}sec".format(res, time.time() - ts)
Categorie:Project Euler, python
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