hashmap

use std::collections::HashMap;
use std::hash::Hash;
use std::sync::{Arc, RwLock};

pub struct Memoizer<K, V> {
    store: RwLock<HashMap<K, Arc<V>>>,

use std::collections::HashMap;
use std::hash::Hash;

const NIL: usize = usize::MAX;

struct Node<K, V> {