Merge pull request #9 from TomPlum/feature/lcm

Math | Added LCM to CollectionExtensions.kt

build.gradle.kts

@@ -28,7 +28,7 @@ subprojects {
     apply(plugin = "maven-publish")
 
     ext {
-        set("releaseVersion", "2.3.1")
+        set("releaseVersion", "2.4.0")
     }
 
     repositories {

library/src/main/kotlin/io/github/tomplum/libs/extensions/CollectionExtensions.kt

@@ -73,3 +73,28 @@ fun <T> List<T>.cartesianProductCubic(second: List<T>, third: List<T>): List<Tri
 private fun <T> cartesianProduct(vararg sets: List<T>): List<List<T>> = sets.fold(listOf(listOf())) { acc, set ->
     acc.flatMap { list -> set.map { element -> list + element } }
 }
+
+/**
+ * Calculates the lowest common multiple of
+ * all the long values of this given list.
+ */
+fun List<Long>.lcm(): Long {
+    if (this.isNotEmpty()) {
+        var result = this[0]
+        this.forEachIndexed { i, _ -> result = lcm(result, this[i]) }
+        return result
+    }
+
+    throw IllegalArgumentException("Cannot find the LCM of an empty list.")
+}
+
+private fun lcm(a: Long, b: Long) = a * (b / gcd(a, b))
+
+private fun gcd(a: Long, b: Long): Long {
+    var n1 = a
+    var n2 = b
+    while (n1 != n2) {
+        if (n1 > n2) n1 -= n2 else n2 -= n1
+    }
+    return n1
+}

library/src/test/kotlin/io/github/tomplum/libs/extensions/CollectionExtensionsTest.kt

@@ -6,6 +6,7 @@ import assertk.assertions.isEmpty
 import assertk.assertions.isEqualTo
 import org.junit.jupiter.api.Nested
 import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
 
 class CollectionExtensionsTest {
     @Nested
@@ -103,4 +104,28 @@ class CollectionExtensionsTest {
             return binary
         }
     }
+
+    @Nested
+    inner class LowestCommonMultiple {
+        @Test
+        fun twoValues() {
+            val values = listOf(4L, 2L)
+            val lcm = values.lcm()
+            assertThat(lcm).isEqualTo(4)
+        }
+
+        @Test
+        fun oneValue() {
+            val values = listOf(10L)
+            val lcm = values.lcm()
+            assertThat(lcm).isEqualTo(10)
+        }
+
+        @Test
+        fun emptyList() {
+            val values = listOf<Long>()
+            val e = assertThrows<IllegalArgumentException> { values.lcm()  }
+            assertThat(e.message).isEqualTo("Cannot find the LCM of an empty list.")
+        }
+    }
 }