Project Euler - Problem 8: Largest Product in a Series

The four adjacent digits in the 1000-digit number that have the greatest product ar 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?

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Explanation

Simply take all numbers in the length of the series, multiple them together and if they are greater than the current largest product, replace it.

Solution #1

private static void Problem8(string series, int seriesLength)
{
    int position = 0;
    ulong largestProduct = 0;
    string productString;
    
    while(position + seriesLength < series.Length)
    {
        productString = series.Substring(position, seriesLength);
        ulong product = 1;
        
        foreach(char value in productString)
        {
            product *= (ulong)char.GetNumericValue(value);   
        }
        
        if(product > largestProduct)
        {
            largestProduct = product;   
        }
        
        position++;
    }
    
    Console.WriteLine(largestProduct);
}

An example of which can be found here.

The average tick time is approximately 415000 ticks. This falls in the average range of the problems we have done before.

Solution #2:

The previous solution can be "improved" upon by not even calculating the product if there is a 0 in the substring because it will never be greater than our default value of 0 assigned to largestProduct initially.

private static void Problem8(string series, int seriesLength)
{
    int position = 0;
    ulong largestProduct = 0;
    string productString;
    
    while(position + seriesLength < series.Length)
    {
        productString = series.Substring(position, seriesLength);
        
        if(productString.Contains("0"))
        {
            position++;
            continue;
        }

        ulong product = 1;
        
        foreach(char value in productString)
        {
            product *= (ulong)char.GetNumericValue(value);   
        }
        
        if(product > largestProduct)
        {
            largestProduct = product;   
        }
        
        position++;
    }
    
    Console.WriteLine(largestProduct);
}

An example of which can be found here.

This is not really a performance boost improvement however. The average tick time is approximately 408000 ticks.

Summary:

We were not really able to optimize our original solution much in this one. If you have any additional improvements, let me know.