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Problem #8: Largest product in a series

ProjectEuler link Hackerrank link

The Problem (Hackerrank version)

Find the greatest product of K consecutive digits in the N digit number.

Input Format

First line contains T that denotes the number of test cases. First line of each test case will contain two integers N & K. Second line of each test case will contain a N digit integer.

Constraints

$$1 \le T \le 100 <br />$$ $$1 \le K \le 7 <br />$$ $$K \le N \le 1000$$

Output Format

Print the required answer for each test case.

Sample Input 0

2
10 5
3675356291
10 5
2709360626

Sample Output 0

3150
0

Explanation 0

• For 3675356291 and selecting K=5 consequetive digits, we have 36753, 67535, 75356, 53562, 35629 and 56291. Where 6 x 7 x 5 x 3 x 5 gives maximum product as 3150
• For 2709360626, 0 lies in all selection of 5 consequetive digits hence maximum product remains 0

Solution (Original problem)

Code (C#)

string number = 
    "73167176531330624919225119674426574742355349194934" +
    "96983520312774506326239578318016984801869478851843" +
    "85861560789112949495459501737958331952853208805511" +
    "12540698747158523863050715693290963295227443043557" +
    "66896648950445244523161731856403098711121722383113" +
    "62229893423380308135336276614282806444486645238749" +
    "30358907296290491560440772390713810515859307960866" +
    "70172427121883998797908792274921901699720888093776" +
    "65727333001053367881220235421809751254540594752243" +
    "52584907711670556013604839586446706324415722155397" +
    "53697817977846174064955149290862569321978468622482" +
    "83972241375657056057490261407972968652414535100474" +
    "82166370484403199890008895243450658541227588666881" +
    "16427171479924442928230863465674813919123162824586" +
    "17866458359124566529476545682848912883142607690042" +
    "24219022671055626321111109370544217506941658960408" +
    "07198403850962455444362981230987879927244284909188" +
    "84580156166097919133875499200524063689912560717606" +
    "05886116467109405077541002256983155200055935729725" +
    "71636269561882670428252483600823257530420752963450";

List<long> ListOfProducts = new List<long>();

for (int i = 0; i < 988; ++i)
    ListOfProducts.Add(IloczynLiczby(number[i].ToString() + number[i+1].ToString() + number[i + 2].ToString()
 + number[i + 3].ToString() + number[i + 4].ToString() + number[i + 5].ToString() + number[i + 6].ToString()
 + number[i + 7].ToString() + number[i + 8].ToString() + number[i + 9].ToString() + number[i + 10].ToString()
 + number[i + 11].ToString() + number[i + 12].ToString()));

ListOfProducts.Sort();
Console.WriteLine(ListOfProducts[ListOfProducts.Count-1]);

long IloczynLiczby(string liczba)
{
    return long.Parse(liczba[0].ToString())
        * long.Parse(liczba[1].ToString())
        * long.Parse(liczba[2].ToString())
        * long.Parse(liczba[3].ToString())
        * long.Parse(liczba[4].ToString())
        * long.Parse(liczba[5].ToString())
        * long.Parse(liczba[6].ToString())
        * long.Parse(liczba[7].ToString())
        * long.Parse(liczba[8].ToString())
        * long.Parse(liczba[9].ToString())
        * long.Parse(liczba[10].ToString())
        * long.Parse(liczba[11].ToString())
        * long.Parse(liczba[12].ToString());
}

Explanation

Another simple problem, we brute force it. We save every possible set of 13-sequence numbers to ListOfProducts. Afterwards, we calculate the product in IloczynLiczby. Finally, sort the list to get it chronogically and print the last entry.

Solution (Hackerrank)

Code (C#)

int t = Convert.ToInt32(Console.ReadLine());
for (int a0 = 0; a0 < t; a0++)
{
    string[] tokens_n = Console.ReadLine().Split(' ');
    int n = Convert.ToInt32(tokens_n[0]);
    int k = Convert.ToInt32(tokens_n[1]);
    string num = Console.ReadLine();

    List<long> ListOfProducts = new List<long>();
            
    for (int i = 0; i < num.Length - k + 1; ++i) {
        string sequence = "";
        
        for (int j = 0; j < k; ++j)
            sequence += num[i + j].ToString();
        
        ListOfProducts.Add(IloczynLiczby(sequence, k));
    }
    
    ListOfProducts.Sort();
    Console.WriteLine(ListOfProducts[ListOfProducts.Count-1]);
}

long IloczynLiczby(string liczba, int k)
{
    long number = 1;
    
    for (int i = 0; i < k; ++i) 
        number *= long.Parse(liczba[i].ToString());
    
    return number;
}

Explanation

Another simple problem, we brute force it. For every n-digit number we save every possible set of k-sequence numbers to ListOfProducts. Afterwards, we calculate the product in IloczynLiczby. Finally, sort the list to get it chronogically and print the last entry.