Lua Implementation of Problem 8

View source code here on GitHub!

Solution

solution()

Returns:

The solution to problem 8

Return type:

number

-- Project Euler Problem 8
--
-- Problem:
--
-- 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?

return {
    solution = function()
        local str = ("73167176531330624919225119674426574742355349194934"
                  .. "96983520312774506326239578318016984801869478851843"
                  .. "85861560789112949495459501737958331952853208805511"
                  .. "12540698747158523863050715693290963295227443043557"
                  .. "66896648950445244523161731856403098711121722383113"
                  .. "62229893423380308135336276614282806444486645238749"
                  .. "30358907296290491560440772390713810515859307960866"
                  .. "70172427121883998797908792274921901699720888093776"
                  .. "65727333001053367881220235421809751254540594752243"
                  .. "52584907711670556013604839586446706324415722155397"
                  .. "53697817977846174064955149290862569321978468622482"
                  .. "83972241375657056057490261407972968652414535100474"
                  .. "82166370484403199890008895243450658541227588666881"
                  .. "16427171479924442928230863465674813919123162824586"
                  .. "17866458359124566529476545682848912883142607690042"
                  .. "24219022671055626321111109370544217506941658960408"
                  .. "07198403850962455444362981230987879927244284909188"
                  .. "84580156166097919133875499200524063689912560717606"
                  .. "05886116467109405077541002256983155200055935729725"
                  .. "71636269561882670428252483600823257530420752963450")
        local answer = 0

        for i = 1,(#str-13) do
            local product = 1
            for j = i,(i+12) do
                product = product * tonumber(str:sub(j, j))
            end

            if product > answer then
                answer = product
            end
        end

        return answer
    end
}