This problem asks us to find the greatest product of five consecutive digits in a given 1000 digit number. First the 1000 digit number has to be stored as a string. I wanted to make sure that each digit of the number was converted from a string to an int only once, which complicates the code a bit. Second, it occurred to me that if I'm looking for the greatest product, I'm also looking for the greatest sum. This allows me to save some further compute time.
function euler8
big_num = "73167176531330624919225119674426574742355349194934...
96983520312774506326239578318016984801869478851843...
85861560789112949495459501737958331952853208805511...
12540698747158523863050715693290963295227443043557...
66896648950445244523161731856403098711121722383113...
62229893423380308135336276614282806444486645238749...
30358907296290491560440772390713810515859307960866...
70172427121883998797908792274921901699720888093776...
65727333001053367881220235421809751254540594752243...
52584907711670556013604839586446706324415722155397...
53697817977846174064955149290862569321978468622482...
83972241375657056057490261407972968652414535100474...
82166370484403199890008895243450658541227588666881...
16427171479924442928230863465674813919123162824586...
17866458359124566529476545682848912883142607690042...
24219022671055626321111109370544217506941658960408...
07198403850962455444362981230987879927244284909188...
84580156166097919133875499200524063689912560717606...
05886116467109405077541002256983155200055935729725...
71636269561882670428252483600823257530420752963450";
sum = 0;
product = 1;
for ii = 1:5
digit(ii) = str2num(big_num(ii));
sum = sum + digit(ii);
product = product*digit(ii);
end
biggest_product = product;
biggest_sum = sum;
for ii = 2:996
sum = sum - digit(1);
for jj = 1:4
digit(jj) = digit(jj+1);
end
digit(5) = str2num(big_num(ii+4));
sum = sum + digit(5);
if sum > biggest_sum
biggest_sum = sum;
biggest_product = digit(1)*digit(2)*digit(3)*digit(4)*digit(5);
end
end
biggest_product