fibonacci with memoization and big integers

fibo_memo_bigint.rs

extern crate num_bigint;

use num_bigint::{BigUint, ToBigUint};
use std::collections::HashMap;

fn fibo(n: BigUint, memo: &mut HashMap<BigUint, BigUint>) -> BigUint {
  let zero = 0.to_biguint().unwrap();
  let one = 1.to_biguint().unwrap();
  let two = 2.to_biguint().unwrap();

  if n == zero || n == one {
    return n
  }

  if let Some(val) = memo.get(&n) {
    return val.clone()
  }

  let ans = fibo(n.clone()-one, memo) + fibo(n.clone()-two, memo);
  memo.insert(n, ans.clone());
  ans
}

fn main() {
  let mut memo: HashMap<BigUint, BigUint> = HashMap::new();

  for i in 90..=100 {
    println!("fibo({}) = {}", i, &mut fibo(i.to_biguint().unwrap(), &mut memo));
  }
}