projecteuler.net/053/src/main.rs

use num_bigint::BigUint;
use num_traits::{Zero, One};

// Calculate large fibonacci numbers.
fn fc(n: usize) -> BigUint {
    let mut nn = n;
    let mut res: BigUint = One::one();

    while nn > 1 {
        res *= nn;
        nn-=1;
    }

    return res;
}

fn bn(n: usize, r: usize) -> BigUint {
    return fc(n) / (fc(r) * fc(n-r));
}


fn main() {
    //println!("Hello, world!");
    //println!("fib(1000) = {}", fib(1000));
    let mut count = 0;
    for n in 1..=100 {
        for r in 1..=n {
            if bn(n, r) > BigUint::from(1000000u32) {
                count +=1;
            }
        }
    }
    println!("{}", count);
}