# Project Euler #8: Largest product in a series

This article is part of a series where I'll be diving head first into the Project Euler puzzles. I want to document the challenge of solving such a puzzle and how I got to the answer. I want to prefix this by stating that I can't cheat for any of these challenges; with that I mean I can't look up any other implementations online. After the implementation, I will validate the answer by using this document or a similar sheet.

You’re given a 1000-digit number, which adjacent 13 digit string of numbers have the greatest product? This is fairly simple:

``````fn problem_8() -> u64 {
let big_digit =
"73167176531330624919225119674426574742355349194934\
96983520312774506326239578318016984801869478851843\
85861560789112949495459501737958331952853208805511\
12540698747158523863050715693290963295227443043557\
66896648950445244523161731856403098711121722383113\
62229893423380308135336276614282806444486645238749\
30358907296290491560440772390713810515859307960866\
70172427121883998797908792274921901699720888093776\
65727333001053367881220235421809751254540594752243\
52584907711670556013604839586446706324415722155397\
53697817977846174064955149290862569321978468622482\
83972241375657056057490261407972968652414535100474\
82166370484403199890008895243450658541227588666881\
16427171479924442928230863465674813919123162824586\
17866458359124566529476545682848912883142607690042\
24219022671055626321111109370544217506941658960408\
07198403850962455444362981230987879927244284909188\
84580156166097919133875499200524063689912560717606\
05886116467109405077541002256983155200055935729725\
71636269561882670428252483600823257530420752963450";

let mut result = 0;

for i in 0..big_digit.len() - 12 {
let mut n: u64 = 1;
let slice = &big_digit[i..13+i];

for f in slice.chars() {
n *= f.to_digit(10).unwrap() as u64;
}

if n > result {
result = n;
}
}
result
}

#[test]
fn test_problem_8() {
assert_eq!(problem_8(), 23514624000);
}
``````

The full solution is available on GitHub.