Implement day 15 of 2016.

2016/src/common.rs

@@ -29,6 +29,24 @@ pub fn prime_sieve(dest: &mut[bool]) {
     }
 }
 
+/// Greatest common divisor
+pub fn gcd(a: i32, b: i32) -> i32 {
+    if a < b {
+        gcd(b, a)
+    } else {
+        if a % b == 0 {
+            b
+        } else {
+            gcd(a % b, b)
+        }
+    }
+}
+
+/// Least common multiple
+pub fn lcm(a: i32, b: i32) -> i32 {
+    a * b / gcd(a, b)
+}
+
 /// Solution trait
 ///
 /// Every day's solution should implement this function so that it can
@@ -60,4 +78,15 @@ mod tests {
 
         assert_eq!(output, input);
     }
+
+    #[test]
+    fn test_gcd() {
+        assert_eq!(12, gcd(24, 36));
+        assert_eq!(1, gcd(1, 7));
+    }
+
+    #[test]
+    fn test_lcm() {
+        assert_eq!(12, lcm(6, 4));
+    }
 }