ProjectEulerPy/p008.py at master · guoheng/ProjectEulerPy · GitHub

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#

import os,logging
import time
import math
import re

def parse_desc(desc):
    ''' return array of digits from description '''
    fields = desc.split("=======")
    data = re.sub(r'\s+', '', fields[1])
    return [int(x) for x in data]

def main(args):
    description = '''
    Largest product in a series
    Problem 8
    The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.
    =======
    73167176531330624919225119674426574742355349194934
    96983520312774506326239578318016984801869478851843
    85861560789112949495459501737958331952853208805511
    12540698747158523863050715693290963295227443043557
    66896648950445244523161731856403098711121722383113
    62229893423380308135336276614282806444486645238749
    30358907296290491560440772390713810515859307960866
    70172427121883998797908792274921901699720888093776
    65727333001053367881220235421809751254540594752243
    52584907711670556013604839586446706324415722155397
    53697817977846174064955149290862569321978468622482
    83972241375657056057490261407972968652414535100474
    82166370484403199890008895243450658541227588666881
    16427171479924442928230863465674813919123162824586
    17866458359124566529476545682848912883142607690042
    24219022671055626321111109370544217506941658960408
    07198403850962455444362981230987879927244284909188
    84580156166097919133875499200524063689912560717606
    05886116467109405077541002256983155200055935729725
    71636269561882670428252483600823257530420752963450
    =======
    Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?
    '''

    if args.test:
        logging.info('Running test...')
        series_size = 4
    else:
        series_size = 13

    digits = parse_desc(description)

    product = 1
    for d in digits[:series_size]:
        product *= d

    max_product = product
    max_series = digits[:series_size]

    num_digits = len(digits)
    for i in range(1, num_digits-series_size):
        prev_d = digits[i-1]
        next_d = digits[i+series_size-1]
        if prev_d == 0:
            product = 1
            for d in digits[i:i+series_size]:
                product *= d
        else:
            product = product*next_d//prev_d
        if product > max_product:
            max_product = product
            max_series = digits[i:i+series_size]

    solution = 'result: {} from series {}'.format(max_product, max_series)
    logging.info(solution)