如何计算21锈因数

Question

我需要在我的项目中计算21阶乘。

fn factorial(num: u64) -> u64 {
    match num {
        0 => 1,
        1 => 1,
        _ => factorial(num - 1) * num,
    }
}

fn main() {
    let x = factorial(21);
    println!("The value of 21 factorial is {} ", x);
}

但是，运行此代码时，出现错误thread 'main' panicked at 'attempt to multiply with overflow', src\main.rs:5:18。

Answer 1

21！不适合64位int。您需要一些arbitrary precision arithmetic（或bigint）库。