Find the greatest product of five consecutive digits in the 1000-digit number.



In [5]:

    
n = """73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450"""

Naive implementation:

First, we'll generate the consecutive arrays:



In [8]:

    
import re
def group_by_count(b, count):
    for i in range(0, max(0, len(b) - count)):
        yield b[i : i + count]

Then we'll create a function to generate products:



In [9]:

    
def product(a):
    res = 1
    for i in a:
        res *= int(i)
    return res

Finally just calculate:



In [10]:

    
r = 0
for i in group_by_count(re.sub("[^0-9]", "", n), 5):
    r = max(r, product(i))
print (r)

Stream implementation:

Now let's consider that we have a stream, the length of string being unknown:



In [41]:

    
def int_number(element):
    return int(element) if element.isdigit() else None
from collections import deque

r = 1 
l = 5
numbers = deque()
# first collect l - 1 elements
it = iter(n)
l -= 1
try:
    while l != 0:
        element = int_number(next(it))
        if element is not None:
            r *= element
            numbers.append(element)
            l -= 1
except Exception as not_enough_elements:
    r = None
    
# then at each new element we can just calculate
try:
    last_l_product = r
    while True:
        element = int_number(next(it))
        if element is not None:
            numbers.append(element)
            cur = product(numbers)
            numbers.popleft()
            r = max(r, cur)
except Exception as ignored:
    pass
print(r)