projecteuler.net/044/main.rs

use std::collections::HashSet;

fn main() {
    let mut hs = HashSet::new();
    for n in 1..10000 {
        let pn = n * ( 3*n -1 ) / 2;
        hs.insert(pn);
    }
    let mut D = 10000000;
    for p in hs.iter() {
        for q in hs.iter() {
            if q <= p {
                continue;
            }
        
            let s = *p + *q;
            if !hs.contains(&s) {
                continue;
            }
            let d = *q - *p;
            if !hs.contains(&d) {
                continue;
            }
            if d < D {
                D = d;
            }
        }
    }
    println!("{}", D);

}