I am working through the Project Euler problems and I have reached a dead end early - I am almost certain my code is correct and yet my answer is not accepted as correct.
The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 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?
My approach is simple - this is my first go at the problem without any optimization, just to see if I can solve it at all:
#include <string>
#include <iostream>
#include <stdlib.h> // atol ASCII to Integer function
int main(){
std::string digits = "73167176531330624919225119674426574742355349194934";
digits += "96983520312774506326239578318016984801869478851843";
digits += "85861560789112949495459501737958331952853208805511";
digits += "12540698747158523863050715693290963295227443043557";
digits += "66896648950445244523161731856403098711121722383113";
digits += "62229893423380308135336276614282806444486645238749";
digits += "30358907296290491560440772390713810515859307960866";
digits += "70172427121883998797908792274921901699720888093776";
digits += "65727333001053367881220235421809751254540594752243";
digits += "52584907711670556013604839586446706324415722155397";
digits += "53697817977846174064955149290862569321978468622482";
digits += "83972241375657056057490261407972968652414535100474";
digits += "82166370484403199890008895243450658541227588666881";
digits += "16427171479924442928230863465674813919123162824586";
digits += "17866458359124566529476545682848912883142607690042";
digits += "24219022671055626321111109370544217506941658960408";
digits += "07198403850962455444362981230987879927244284909188";
digits += "84580156166097919133875499200524063689912560717606";
digits += "05886116467109405077541002256983155200055935729725";
digits += "71636269561882670428252483600823257530420752963450";
long product = 1;
long temp = 1;
for(int i = 12; i < digits.length(); i++){
for(int j = 0; j<13; j++){
temp = temp*atoi(digits.substr(i-j,1).c_str());
}
if(temp > product){
product = temp;
std::cout << "index: " << (i-12) << " Product: " << product << "\n";
}
temp = 1;
}
return 0;
}
This returns the following answers:
index: 0 Product: 5000940
index: 16 Product: 9797760
index: 19 Product: 13063680
index: 21 Product: 25401600
index: 22 Product: 50803200
index: 23 Product: 71124480
index: 24 Product: 284497920
index: 25 Product: 568995840
index: 40 Product: 1020366720
index: 41 Product: 1632586752
index: 43 Product: 2040733440
index: 503 Product: 2091059712
And so, of course, I submit this last number to the P.E. site, but it is rejected.
I've done the very obvious sanity checking (Do the 13 digits at index 503 actually produce 2091059712?) and yes, they do, so I don't have something subtle where it does the index wrong and only multiplies 12 numbers (or 14) rather than the correct 13.
SO... what could possibly make my code return the wrong number? Do I accidentally multiply by an extra zero without noticing? I've looked at this for an hour now and it's time to get other eyes on my code.
It seems 913 does not fit into long at your platform.
You may replace long with long long int or some other wider integer.
live example gives following output
index: 0 Product: 5000940
index: 16 Product: 9797760
index: 19 Product: 13063680
index: 21 Product: 25401600
index: 22 Product: 50803200
index: 23 Product: 71124480
index: 24 Product: 284497920
index: 25 Product: 568995840
index: 40 Product: 1020366720
index: 41 Product: 1632586752
index: 43 Product: 2040733440
index: 88 Product: 2972712960
index: 195 Product: 6270566400
index: 196 Product: 14108774400
index: 197 Product: 23514624000
Not making such mistakes is exactly what project euler want to teach you.