projecteuler.net/039/main.rs

use std::collections::HashMap;
const SIZE: u32 = 1000u32;

fn squares() -> HashMap<u32, u32> {
    let mut res = HashMap::new();
    for n in 1..=SIZE {
        res.insert(n*n, n);
    }
    res
}
fn main() {
    let mut sq = squares();
    let mut ps = HashMap::new();
    for a in 1..SIZE {
        for b in 1..SIZE {
            let c2 = a*a + b*b;
            if sq.contains_key(&c2) {
                let c = *sq.get(&c2).unwrap();
                let p = a + b + c;
                if p > SIZE { continue; }
                if !ps.contains_key(&p) {
                    ps.insert(p, 1);
                } else {
                    let count = ps.get(&p).unwrap();
                    ps.insert(p, count + 1);
                }
            }
        }
    }
    let mut max_v = 0u32;
    let mut max_k = 0u32;
    for (k, v) in ps.iter() {
        if *v > max_v {
            max_v = *v;
            max_k = *k;
        }
    }
    println!("{}", max_k);
}