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rustlings/solutions/18_iterators/iterators4.rs
2024-08-22 14:41:25 +02:00

72 lines
2 KiB
Rust

// 3 possible solutions are presented.
// With `for` loop and a mutable variable.
fn factorial_for(num: u64) -> u64 {
let mut result = 1;
for x in 2..=num {
result *= x;
}
result
}
// Equivalent to `factorial_for` but shorter and without a `for` loop and
// mutable variables.
fn factorial_fold(num: u64) -> u64 {
// Case num==0: The iterator 2..=0 is empty
// -> The initial value of `fold` is returned which is 1.
// Case num==1: The iterator 2..=1 is also empty
// -> The initial value 1 is returned.
// Case num==2: The iterator 2..=2 contains one element
// -> The initial value 1 is multiplied by 2 and the result
// is returned.
// Case num==3: The iterator 2..=3 contains 2 elements
// -> 1 * 2 is calculated, then the result 2 is multiplied by
// the second element 3 so the result 6 is returned.
// And so on…
#[allow(clippy::unnecessary_fold)]
(2..=num).fold(1, |acc, x| acc * x)
}
// Equivalent to `factorial_fold` but with a built-in method that is suggested
// by Clippy.
fn factorial_product(num: u64) -> u64 {
(2..=num).product()
}
fn main() {
// You can optionally experiment here.
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn factorial_of_0() {
assert_eq!(factorial_for(0), 1);
assert_eq!(factorial_fold(0), 1);
assert_eq!(factorial_product(0), 1);
}
#[test]
fn factorial_of_1() {
assert_eq!(factorial_for(1), 1);
assert_eq!(factorial_fold(1), 1);
assert_eq!(factorial_product(1), 1);
}
#[test]
fn factorial_of_2() {
assert_eq!(factorial_for(2), 2);
assert_eq!(factorial_fold(2), 2);
assert_eq!(factorial_product(2), 2);
}
#[test]
fn factorial_of_4() {
assert_eq!(factorial_for(4), 24);
assert_eq!(factorial_fold(4), 24);
assert_eq!(factorial_product(4), 24);
}
}