Project Euler #8 NOT related to overflow

December 29, 2021

I too am attempting Project Euler #8. I know what the right answer is, but I’m getting something different. I’m using all ulong in a checked block, so this isn’t related to overflow.

Here’s the problem:

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

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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?

And here’s my implementation (using LinqPad). I keep getting an answer of 10077696000 but I know the answer is actually 23514624000;

string digit = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355668966489504452445231617318564030987111217223831136222989342338030813533627661428280644448664523874930358907296290491560440772390713810515859307960866701724271218839987979087922749219016997208880937766572733300105336788122023542180975125454059475224352584907711670556013604839586446706324415722155397536978179778461740649551492908625693219784686224828397224137565705605749026140797296865241453510047482166370484403199890008895243450658541227588666881164271714799244429282308634656748139191231628245861786645835912456652947654568284891288314260769004224219022671055626321111109370544217506941658960408071984038509624554443629812309878799272442849091888458015616609791913387549920052406368991256071760605886116467109405077541002256983155200055935729725716362695618826704282524836008232575304207529634500";


int numDigits = 13;



ulong answer = 0;
int answerIndex = 0;
int currentIndex = 0;
checked
{
    while (currentIndex <= digit.Length - numDigits)
    {
        var substr = digit.Substring(currentIndex, numDigits);
        if (!substr.Contains('0'))
        {
            ulong product = substr.ToCharArray().Select(x => ulong.Parse(x.ToString())).Aggregate((x, y) => x * y);

            if (product > answer)
            {
                answerIndex = currentIndex;
                answer = product;
                var disp = string.Join(" x ", substr.ToCharArray());
                $"Start Index:\t{currentIndex.ToString().PadLeft(4)}\t\tDigits:\t{disp} = {product}".Dump();
            }
        }
        currentIndex++;
    }
}

$"Answer is: {answer}".Dump();

>Solution :

Your argument is incorrect, something went wrong when you copy pasted and you lost 7:

// current code
string digit = "...227443043556689664895044524452316173185640..." 
// should be
string digit = "...2274430435576689664895044524452316173185640..."
                              ^
                              |
                            missed