CodeWars/5kyu/some_egyptians_fractions/solution.rs

use std::cmp::max;
use std::cmp::min;

fn gcd(mut a: u32, mut b: u32) -> u32 {
    while b != 0 {
        let t = b;
        b = a % b;
        a = t;
    }

    a
}

fn lcm(a: u32, b: u32) -> u32 {
    let c = gcd(a, b);

    max(a, b) / c * min(a, b)
}

fn format_fraction(fraction: &(u32, u32)) -> String {
    if fraction.1 == 1 {
        return format!("{}", fraction.0);
    }

    format!("{}/{}", fraction.0, fraction.1)
}

fn decompose(mut num: u32, mut denom: u32) -> String {
    if num == 0 {
        return "".to_string();
    }

    let mut fractions: Vec<(u32, u32)> = Vec::new();

    if num >= denom {
        fractions.push((num / denom, 1));
        num = num % denom;
    }

    let mut running_denom = 2;
    while num > 1 {
        if num * running_denom < denom {
            running_denom += 1;
            continue;
        }

        fractions.push((1, running_denom));

        let new_denom = lcm(denom, running_denom);
        let new_num = (new_denom / denom) * num - new_denom / running_denom;

        num = new_num;
        denom = new_denom;

        running_denom += 1;
    }
    if num >= 1 {
        fractions.push((num, denom));
    }

    fractions
        .iter()
        .map(format_fraction)
        .reduce(|acc, frac| acc + ", " + &frac)
        .unwrap()
}