Project Euler #4: Largest palindrome product
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.
In this article I'll be solving: Project Euler #4.
This little puzzle asks to find the largest palindrome product of two 3-digit numbers. All the 3-digit numbers range from 100 to 999 and the result should be a palindrome. This is fairly easy:
fn is_palindrome(x: u32) -> bool {
let string = x.to_string();
let len = string.len() - 1;
let end = string.len() / 2;
string[0..end]
.chars()
.enumerate()
.all(|(i,n)| n == string.chars().nth(len - i).unwrap())
}
#[test]
fn is_palindrome_test() {
assert_eq!(is_palindrome(1), true);
assert_eq!(is_palindrome(12), false);
assert_eq!(is_palindrome(11), true);
assert_eq!(is_palindrome(101), true);
assert_eq!(is_palindrome(1001), true);
assert_eq!(is_palindrome(10101), true);
}
fn problem_4() -> u32 {
let mut max = 0;
for i in 100..=999 {
for j in 100..=999 {
let product = i * j;
if product > max && is_palindrome(product) {
max = product;
}
}
}
max
}
#[test]
fn test_problem_4() {
assert_eq!(problem_4(), 906609)
}
Voila! The answer is 906609.
The full solution is available on GitHub.
