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/*
* Project Euler: Classic, "Largest product in a series" solution
* Implementation by A. S. "Aleksey" Ahmann <hackermaneia@riseup.net>
* - https://github.com/Alekseyyy
*
* Problem link: https://projecteuler.net/problem=8
* Thanks to StackOverflowers for helping me with that code: https://stackoverflow.com/questions/68245264/inconsitent-behaviour-with-computation-of-greatest-product-given-n-adjacent-d
*/
import std.stdio : writeln;
import std.array : replace;
import std.conv : to;
string number = "73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450";
void main() {
number = replace(number, "\n", "");
long[] x = format_adjacent(number);
long largest_product = largestProduct(x, 13);
writeln(largest_product);
}
long[] format_adjacent(string number) {
long[] adjacent_numbers;
for (long i = 0; i < number.length; i++)
adjacent_numbers ~= to!long(number[i] - to!char("0"));
return adjacent_numbers;
}
long computeProduct(long[] sequence) {
long product = sequence[0];
for (long i = 1; i < sequence.length; i++)
product = product * sequence[i];
return product;
}
long largestProduct(long[] sequence, long slice) {
long largest_product = 0;
long n = 0;
long fin = to!long(sequence.length) - (slice - 1);
while (n < fin) {
long[] seq = sequence[n .. n + slice];
long product = computeProduct(seq);
if (product > largest_product)
largest_product = product;
n = n + 1;
}
return largest_product;
}
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