Shared via Rust Playground

playground.rs

use std::collections::HashMap;

#[derive(Clone, Debug)]
struct Data {
    values: Vec<i32>,
    pass_to: Option<usize>,
}

impl Data {
    fn has_complete_values(&self) -> bool {
        self.values.len() == 2
    }
}

fn get_data() -> HashMap<usize, Data> {
    let mut data = HashMap::new();
    
    data.insert(1, Data{ values: vec![3, 2], pass_to: Some(2) });
    data.insert(2, Data{ values: vec![1], pass_to: Some(4) });
    data.insert(3, Data{ values: vec![5, 9], pass_to: Some(4) });
    data.insert(4, Data{ values: vec![], pass_to: None });
    data
}


fn main() {
    let mut data = get_data();
    loop {
        if data.values().all(|d| d.has_complete_values()) {
            break;
        }
        
        let mut mutable_data = data.clone();
        for d in data.values() {
            if d.has_complete_values() {
                if let Some(pass_to) = d.pass_to {
                    let value = d.values[0];
                    let entry = mutable_data.get_mut(&pass_to).unwrap();
                    if !entry.values.contains(&value) && !entry.has_complete_values() {
                        entry.values.push(value);
                    }
                }
            }
        }
        data = mutable_data;
    }
    println!("{:#?}", data);
}