projecteuler.net/050/main.rs

use std::collections::HashSet;
use std::env;

fn er() -> Vec<u64> {
    let mut nums = Vec::new();
    let size = 4000000;
    for n in 0..size+1 { nums.push(true); }
    let mut p = 1;
    loop {
        let mut found = false;
        for i in p+1..size {
            if nums[i] {
                found = true;
                p = i;
                break;
            }
        }
        if !found { break; }
        for i in (2 * p .. size).step_by(p) {
            nums[i] = false;
        }
    }
    let mut res = Vec::new();
    for i in 2..size {
        if nums[i] { res.push(i as u64); }
    }
    return res;
}

fn span(l: usize, ps: &Vec<u64>, hs: &HashSet<u64>) -> u64 {
    let mut sum = 0u64;
    let mut max = 0u64;
    
    for i in 0..ps.len() {
        sum += ps.get(i).unwrap();
        if i >= l {
            sum -= ps.get(i - l).unwrap();
        }
        if sum > 1000000 {
            continue;
        }
        if hs.contains(&sum) && i >= l {
            if sum > max {
                max = sum;
            }
        }
    }
    return max;
}

fn main() {
    //env::set_var("RUST_BACKTRACE", "full");
    let ps = er();
    let mut hs = HashSet::new();
    for p in ps.iter() {
        hs.insert(*p);
    }
    let mut max = 0;
    //let mut l_max = 0;
    for s in 1..ps.len() - 1 {
        let m = span(s, &ps, &hs);
        if m > 0 {
            //l_max = s;
            max = m;
            println!("{} {}", s, m);
        }
    }

    println!("{}", max);

}