Part 2 of the rmotr.com python scholarship. C++ program that takes a large number formatted as a string and finds the biggest product of n adjacent digits within the string.

adjacentDigitsProduct

#include <iostream>
#include <string>
#include <vector>

unsigned long long int adjDigProduct(std::vector<int> NUMB, int digits, unsigned long long int biggest);
std::vector<int> vectorify(std::string s);

int main()
{
    //initialize variables
    unsigned long long int biggest = 0;
    const std::string input = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450";
    int numDigits;

    //receive input
    std::cout << "How many adjacent digits?\n";
    std::cin >> numDigits;

    //output
    std::cout << "The biggest product for " << numDigits << " digits is " << adjDigProduct(vectorify(input), numDigits, biggest) << "\n";
}

unsigned long long int adjDigProduct(std::vector<int> NUMB, int digits, unsigned long long int biggest)
{
    //test base case, reached the end of the vector
    if (NUMB.size() < digits)
        return biggest;

    unsigned long long int product = 1;

    //multiply "digits"-number of elements of the vector together
    for (int i = 0; i < digits; i++)
        product *= NUMB[i];

    //remove the first element of the vector for recursion
    NUMB.erase(NUMB.begin());

    //if our new product is bigger than the previous biggest, send it instead
    if (product > biggest)
        return adjDigProduct(NUMB, digits, product);
    else
        return adjDigProduct(NUMB, digits, biggest);
}

//converts a string of single-digit numbers with no delimiters into a vector of integers
std::vector<int> vectorify(std::string s)
{
    std::vector<int> v;

    for (int i = 0; i < s.length(); i++)
        v.push_back((s.at(i) - '0'));

    return v;
}

/*
TEST INPUT:
7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450

SAMPLE OUTPUT:
How many adjacent digits?
4
The biggest product for 4 digits is 5832

How many adjacent digits?
5
The biggest product for 5 digits is 40824

How many adjacent digits?
13
The biggest product for 13 digits is 23514624000

How many adjacent digits?
17
The biggest product for 17 digits is 5292994896000

How many adjacent digits?
25
The biggest product for 25 digits is 94810963968000000

How many adjacent digits?
50
The biggest product for 50 digits is 17371650400163201024
*/