Adds simple solution in kotlin for the sum of multiples problem

Author: Bruno Ferreira

kotlin/sum-of-multiples/README.md

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+# Sum Of Multiples
+
+Given a number, find the sum of all the unique multiples of particular numbers up to
+but not including that number.
+
+If we list all the natural numbers below 20 that are multiples of 3 or 5,
+we get 3, 5, 6, 9, 10, 12, 15, and 18.
+
+The sum of these multiples is 78.
+## Source
+
+A variation on Problem 1 at Project Euler [http://projecteuler.net/problem=1](http://projecteuler.net/problem=1)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

kotlin/sum-of-multiples/build.gradle

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+buildscript {
+  ext.kotlin_version = '1.2.40'
+  repositories {
+    mavenCentral()
+  }
+  dependencies {
+    classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+  }
+}
+
+apply plugin: 'kotlin'
+
+repositories {
+  mavenCentral()
+}
+
+dependencies {
+  compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
+
+  testCompile 'junit:junit:4.12'
+  testCompile "org.jetbrains.kotlin:kotlin-test-junit:$kotlin_version"
+}
+test {
+  testLogging {
+    exceptionFormat = 'full'
+    events = ["passed", "failed", "skipped"]
+  }
+}

kotlin/sum-of-multiples/src/main/kotlin/SumOfMultiples.kt

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+object SumOfMultiples {
+    fun sum(multiplesOf: Set<Int>, upTo: Int): Int {
+        return (1..(upTo - 1)).filter { n ->
+            multiplesOf.indexOfFirst { m ->
+                n % m == 0
+            } > -1
+        }.sum()
+    }
+}

kotlin/sum-of-multiples/src/test/kotlin/SumOfMultiplesTest.kt

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+import org.junit.Ignore
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class SumOfMultiplesTest {
+
+    @Test
+    fun `multiples of 3 or 5 up to 1`() {
+        assertEquals(0, SumOfMultiples.sum(setOf(3, 5), 1))
+    }
+
+    @Test
+    fun `multiples of 3 or 5 up to 4`() {
+        assertEquals(3, SumOfMultiples.sum(setOf(3, 5), 4))
+    }
+
+    @Test
+    fun `multiples of 3 up to 7`() {
+        assertEquals(9, SumOfMultiples.sum(setOf(3), 7))
+    }
+
+    @Test
+    fun `multiples of 3 or 5 up to 10`() {
+        assertEquals(23, SumOfMultiples.sum(setOf(3, 5), 10))
+    }
+
+    @Test
+    fun `multiples of 3 or 5 up to 100`() {
+        assertEquals(2318, SumOfMultiples.sum(setOf(3, 5), 100))
+    }
+
+    @Test
+    fun `multiples of 3 or 5 up to 1000`() {
+        assertEquals(233168, SumOfMultiples.sum(setOf(3, 5), 1000))
+    }
+
+    @Test
+    fun `multiples of 7, 13 or 17 up to 20`() {
+        assertEquals(51, SumOfMultiples.sum(setOf(7, 13, 17), 20))
+    }
+
+    @Test
+    fun `multiples of 4 or 6 up to 15`() {
+        assertEquals(30, SumOfMultiples.sum(setOf(4, 6), 15))
+    }
+
+    @Test
+    fun `multiples of 5, 6 or 8 up to 150`() {
+        assertEquals(4419, SumOfMultiples.sum(setOf(5, 6, 8), 150))
+    }
+
+    @Test
+    fun `multiples of 5 or 25 up to 51`() {
+        assertEquals(275, SumOfMultiples.sum(setOf(5, 25), 51))
+    }
+
+    @Test
+    fun `multiples of 43 or 47 up to 10000`() {
+        assertEquals(2203160, SumOfMultiples.sum(setOf(43, 47), 10000))
+    }
+
+    @Test
+    fun `multiples of 1 up to 100`() {
+        assertEquals(4950, SumOfMultiples.sum(setOf(1), 100))
+    }
+
+    @Test
+    fun `multiples of an empty set up to 10000`() {
+        assertEquals(0, SumOfMultiples.sum(emptySet(), 10000))
+    }
+
+}