Problem 8

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

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

Solution

namespace ProjectEulerCSharp_008

{

    class Program

    {

        static void Main(string[] args)

        {

            string digits = @"

                73167176531330624919225119674426574742355349194934

                96983520312774506326239578318016984801869478851843

                85861560789112949495459501737958331952853208805511

                12540698747158523863050715693290963295227443043557

                66896648950445244523161731856403098711121722383113

                62229893423380308135336276614282806444486645238749

                30358907296290491560440772390713810515859307960866

                70172427121883998797908792274921901699720888093776

                65727333001053367881220235421809751254540594752243

                52584907711670556013604839586446706324415722155397

                53697817977846174064955149290862569321978468622482

                83972241375657056057490261407972968652414535100474

                82166370484403199890008895243450658541227588666881

                16427171479924442928230863465674813919123162824586

                17866458359124566529476545682848912883142607690042

                24219022671055626321111109370544217506941658960408

                07198403850962455444362981230987879927244284909188

                84580156166097919133875499200524063689912560717606

                05886116467109405077541002256983155200055935729725

                71636269561882670428252483600823257530420752963450"

            .Replace(" ", "").Replace("\r\n", "");

           

            int answer = 0;

            for(int i = 0; i < digits.Length – 5; i++)

            {

                int digit1 = int.Parse(digits.Substring(i+0, 1));

                int digit2 = int.Parse(digits.Substring(i+1, 1));

                int digit3 = int.Parse(digits.Substring(i+2, 1));

                int digit4 = int.Parse(digits.Substring(i+3, 1));

                int digit5 = int.Parse(digits.Substring(i+4, 1));

                int product = digit1*digit2*digit3*digit4*digit5;

                if(product > answer) { answer = product; }

            }

            System.Console.WriteLine(answer);

        }

    }

}

Discussion

I’m not sure what the ‘trick’ with this problem was supposed to be.  Even when this problem was posted (a little over 9 years ago) it probably only took a fraction of a second.  I suppose converting a character digit to an integer used to be a bit of a novelty.  Something like int digit = chardigit – ‘0’ would give you the results you want. 

If you have any questions, leave a comment, find me on Twitter (@azzlsoft) or email (rich@azzlsoft.com).