Solve day 8

src/lib.rs

@@ -1,5 +1,8 @@
-use std::fmt::{Debug, Display};
-use std::str::FromStr;
+use std::{
+    fmt::{Debug, Display},
+    ops::{Div, Mul, Rem},
+    str::FromStr,
+};
 
 /// Parse a whitespace separated list of things.
 ///
@@ -27,3 +30,46 @@ where
 {
     format!("{a}{b}").parse().unwrap()
 }
+
+/// Return the greatest common divisor.
+///
+/// https://en.wikipedia.org/wiki/Euclidean_algorithm
+pub fn gcd<T>(mut a: T, mut b: T) -> T
+where
+    T: PartialEq + Default + Rem<Output = T> + Copy,
+{
+    let zero = T::default();
+    while b != zero {
+        (a, b) = (b, a % b);
+    }
+
+    a
+}
+
+/// Return the least common multiple.
+///
+/// https://en.wikipedia.org/wiki/Least_common_multiple
+pub fn lcm<T>(a: T, b: T) -> T
+where
+    T: PartialEq + Default + Rem<Output = T> + Div<Output = T> + Mul<Output = T> + Copy,
+{
+    let gcd = gcd(a, b);
+    a / gcd * b
+}
+
+#[cfg(test)]
+mod test {
+    use crate::*;
+
+    #[test]
+    fn test_gcd() {
+        assert_eq!(gcd(252, 105), 21);
+        assert_eq!(gcd(105, 252), 21);
+    }
+
+    #[test]
+    fn test_lcm() {
+        assert_eq!(lcm(4, 6), 12);
+        assert_eq!(lcm(6, 4), 12);
+    }
+}