add bench for lcm

2023/src/bin/day08.rs

@@ -51,7 +51,7 @@ fn part1(parsed: &Parsed) -> usize {
 // I assume this holds true for other inputs (it can’t have been random),
 // but I don’t see it anywhere in the task and only found out by experimentation.
 fn part2(parsed: &Parsed) -> usize {
-    parsed.1.keys().filter(|start| start.ends_with("A")).map(|start| steps_until(parsed, start, "Z")).fold(1, |acc, n| lcm(acc, n))
+    parsed.1.keys().filter(|start| start.ends_with("A")).fold(1, |acc, n| lcm(acc, steps_until(parsed, n, "Z")))
 }
 
 #[cfg(test)]

2023/src/common.rs

@@ -1,3 +1,4 @@
+extern crate test;
 use std::{
     fmt::Display,
     iter::Step,
@@ -82,3 +83,20 @@ fn gcd(mut x: usize, mut y: usize) -> usize {
 pub fn lcm(x: usize, y: usize) -> usize {
     x * y / gcd(x, y)
 }
+
+#[cfg(test)]
+mod benches {
+    use std::hint::black_box;
+
+    use super::*;
+
+    #[bench]
+    fn bench_lcm(b: &mut test::Bencher) {
+        b.iter(|| assert_eq!(lcm(black_box(20513), black_box(18827)), 1374371))
+    }
+
+    #[bench]
+    fn bench_lcm_big(b: &mut test::Bencher) {
+        b.iter(|| assert_eq!(lcm(black_box(169433831251), black_box(22199)), 13385272668829))
+    }
+}