Snippet

project_euler/8.rb

Code:

# Project Euler Problem 8: Largest Product in a Series

# https://projecteuler.net/problem=8

# The four adjacent digits in the 1000-digit number that have the
# greatest product are 9 × 9 × 8 × 9 = 5832.

    NUM =
    '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?

def solve(n)
    (0..NUM.length - n).map { |m| NUM[m, n].chars.map(&:to_i).inject(:*) }.max
end

puts solve(4)
puts solve(13)

Output:

5832
23514624000