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[英]How do I calculate a multiple factorial using num_bigint in Rust?
[英]How to calculate 21 factorial in Rust?
我需要在我的項目中計算 21 個階乘。
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);
}
運行此代碼時,出現錯誤:
thread 'main' panicked at 'attempt to multiply with overflow', src\main.rs:5:18
一個u64
21! (它在 2^65 和 2^66 之間),但是u128
可以。
一個可能的實現可能是
pub fn factorial(num: u128) -> u128 {
match num {
0 => 1,
1.. => (1..num+1).product(),
}
}
#[test]
fn factorial_of_21() {
assert_eq!(51090942171709440000,factorial(21));
}
我認為實現應該是這樣的
pub fn factorial(num: u128) -> u128 {
(1..=num).product()
}
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