Python/project_euler/problem_008/sol3.py

"""
Project Euler Problem 8: https://projecteuler.net/problem=8

Largest product in a series

The four adjacent digits in the 1000-digit number that have the greatest
product are 9 x 9 x 8 x 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?
"""

import sys

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


def str_eval(s: str) -> int:
    """
    Returns product of digits in given string n

    >>> str_eval("987654321")
    362880
    >>> str_eval("22222222")
    256
    """

    product = 1
    for digit in s:
        product *= int(digit)
    return product


def solution(n: str = N) -> int:
    """
    Find the thirteen adjacent digits in the 1000-digit number n that have
    the greatest product and returns it.
    """

    largest_product = -sys.maxsize - 1
    substr = n[:13]
    cur_index = 13
    while cur_index < len(n) - 13:
        if int(n[cur_index]) >= int(substr[0]):
            substr = substr[1:] + n[cur_index]
            cur_index += 1
        else:
            largest_product = max(largest_product, str_eval(substr))
            substr = n[cur_index : cur_index + 13]
            cur_index += 13
    return largest_product


if __name__ == "__main__":
    print(f"{solution() = }")