Problem 8: Largest Product in a Series

Problem

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Solution

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//* Problem 8: Largest Product in a Series
//*
//* the four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.
// the number has been omitted for brevity. see NUMBER
//* Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?

//! time complexity: O(n)
//! where n is the length of the input string
use euler::prelude::*;

const NUMBER: &str = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450";

fn solve() -> Solution {
    let digits: Vec<u32> = NUMBER
        .chars()
        .map(|c| c.to_digit(10))
        .collect::<Option<_>>()
        .unwrap();
    let mut max_product = 0;

    for window in digits.windows(13) {
        let product = window.iter().map(|&d| d as u64).product::<_>();
        max_product = max_product.max(product);
    }

    solution!(max_product)
}

problem!(
    8,
    solve,
    "b9fb30b6553415e9150051ce5710a93d0f55b22557c0068d8e16619a388f145a"
);