08-Largest-Product-In-a-Series/productofdigits.c


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#include <stdlib.h>
#include <stdio.h>

const char bigBoy[1001] = "73167176531330624919225119674426574742355349194934"
    "96983520312774506326239578318016984801869478851843"
    "85861560789112949495459501737958331952853208805511"
    "12540698747158523863050715693290963295227443043557"
    "66896648950445244523161731856403098711121722383113"
    "62229893423380308135336276614282806444486645238749"
    "30358907296290491560440772390713810515859307960866"
    "70172427121883998797908792274921901699720888093776"
    "65727333001053367881220235421809751254540594752243"
    "52584907711670556013604839586446706324415722155397"
    "53697817977846174064955149290862569321978468622482"
    "83972241375657056057490261407972968652414535100474"
    "82166370484403199890008895243450658541227588666881"
    "16427171479924442928230863465674813919123162824586"
    "17866458359124566529476545682848912883142607690042"
    "24219022671055626321111109370544217506941658960408"
    "07198403850962455444362981230987879927244284909188"
    "84580156166097919133875499200524063689912560717606"
    "05886116467109405077541002256983155200055935729725"
    "71636269561882670428252483600823257530420752963450";
// parseNum: Splits in segements of r, to find out the largest product of digits
// for that segment size
// max is the maximum product found within the number
// x: the number (as a char string) to be parsed
// r: the range to parse over
long long parseNum(const char *x, int r){
    int len = 1000;
    long max; 
    for(int i = 0; i < len - r; i++){
        // Digits in ascii start at 48
        long long prod =  (x[i] - 48);
        for(int k = i + 1; k < i + r; k++)
            prod *= (x[k] - 48);
        if(prod > max)
            max = prod;
    }
    return max;
}


int main(){
    long long p = parseNum(bigBoy, 13);
    printf("%ld\n", p);
    //printf("%ld\n", parseNum(bigBoy, 13));
    return 0;
}