Added anagram verifier

DIRECTORY.md

@@ -37,6 +37,8 @@
         * [Mergesort](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/sort/MergeSort.kt)
         * [Quicksort](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/sort/QuickSort.kt)
         * [Selectionsort](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/sort/SelectionSort.kt)
+      * String
+        * [Anagram](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/string/Anagram.kt) 
   * Test
       * Dynamic Programming
         * [Palindromepartitioningtest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/dynamic_programming/PalindromePartitioningTest.kt)
@@ -72,3 +74,5 @@
         * [Mergesorttest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/sort/MergeSortTest.kt)
         * [Quicksorttest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/sort/QuickSortTest.kt)
         * [Selectionsorttest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/sort/SelectionSortTest.kt)
+      * String
+        * [AnagramTest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/string/AnagramTest.kt)

src/main/kotlin/string/Anagram.kt

@@ -0,0 +1,48 @@
+package string
+
+
+/**
+ * This method implements a simple anagram verifier algorithm
+ *
+ * @param string The string to be compared with
+ * @param ignoreWhitespace true if whitespaces should be ignored
+ * @param ignoreCase true if casing should be ignored
+ *
+ * Worst-case performance       O(n)
+ * Best-case performance        O(n)
+ * Average performance	        O(n)
+ * Worst-case space complexity	O(N)
+ **/
+fun String.isAnagramOf(string: String, ignoreWhitespace: Boolean = true, ignoreCase: Boolean = true): Boolean {
+    val string1 = this.normalize(ignoreWhitespace, ignoreCase)
+    val string2 = string.normalize(ignoreWhitespace, ignoreCase)
+
+    if (string1.length != string2.length)
+        return false
+
+    val charMap1 = string1.toCharCountMap()
+    val charMap2 = string2.toCharCountMap()
+
+    return charMap1 == charMap2
+}
+
+private fun String.toCharCountMap(): Map<Char, Int> {
+    val charMap = mutableMapOf<Char, Int>()
+
+    this.forEach {
+        val count = charMap[it] ?: 0
+        charMap[it] = count + 1
+    }
+
+    return charMap
+}
+
+private fun Sequence<Char>.removeWhitespaces() = this.filter { it.isWhitespace().not() }
+
+private fun Sequence<Char>.toLowerCase() = this.map { it.toLowerCase() }
+
+private fun String.normalize(ignoreWhitespace: Boolean, ignoreCase: Boolean) = this
+    .asSequence()
+    .let { if (ignoreCase) it.toLowerCase() else it }
+    .let { if (ignoreWhitespace) it.removeWhitespaces() else it }
+    .joinToString("")

src/test/kotlin/string/AnagramTest.kt

@@ -0,0 +1,95 @@
+package string
+
+import org.junit.Test
+
+
+class AnagramTest {
+
+    @Test
+    fun `test isAnagramOf empty string returns true`() {
+        val string1 = ""
+        val string2 = ""
+
+        assert(string1.isAnagramOf(string2))
+    }
+
+    @Test
+    fun `test isAnagramOf single letter string returns true`() {
+        val string1 = "a"
+        val string2 = "a"
+
+        assert(string1.isAnagramOf(string2))
+    }
+
+    @Test
+    fun `test isAnagramOf returns true`() {
+        val string1 = "testIsAnagramOfReturnsTrue1"
+        val string2 = "test isAnagramOf returns true 1"
+
+        assert(string1.isAnagramOf(string2))
+    }
+
+    @Test
+    fun `test isAnagramOf ignoreWhitespace true ignoreCase True returns True`() {
+        val string1 = "Wolfgang Amadeus Mozart"
+        val string2 = "A famous german waltz god"
+
+        assert(string1.isAnagramOf(string2, ignoreWhitespace = true, ignoreCase = true))
+    }
+
+    @Test
+    fun `test isAnagramOf ignoreWhitespace False ignoreCase True returns True`() {
+        val string1 = "Eleven plus Two"
+        val string2 = "Twelve plus One"
+
+        assert(string1.isAnagramOf(string2, ignoreWhitespace = false, ignoreCase = true))
+    }
+
+    @Test
+    fun `test isAnagramOf ignoreWhitespace True ignoreCase False returns True`() {
+        val string1 = "wolfgang amadeus mozart"
+        val string2 = "a famous german waltz god"
+
+        assert(string1.isAnagramOf(string2, ignoreWhitespace = true, ignoreCase = false))
+    }
+
+    @Test
+    fun `test isAnagramOf ignoreWhitespace False ignoreCase False returns True`() {
+        val string1 = "wolfgangamadeusmozart"
+        val string2 = "afamousgermanwaltzgod"
+
+        assert(string1.isAnagramOf(string2, ignoreWhitespace = false, ignoreCase = false))
+    }
+
+    @Test
+    fun `test isAnagramOf ignoreWhitespace true ignoreCase True returns False`() {
+        val string1 = "testIsAnagramOfReturnsTrue1"
+        val string2 = "test isAnagramOf returns true 2"
+
+        assert(string1.isAnagramOf(string2, ignoreWhitespace = true, ignoreCase = true).not())
+    }
+
+    @Test
+    fun `test isAnagramOf ignoreWhitespace False ignoreCase True returns False`() {
+        val string1 = "testIsAnagramOfReturnsTrue1"
+        val string2 = "test IsAnagramOf Returns True 1"
+
+        assert(string1.isAnagramOf(string2, ignoreWhitespace = false, ignoreCase = true).not())
+    }
+
+    @Test
+    fun `test isAnagramOf ignoreWhitespace True ignoreCase False returns False`() {
+        val string1 = "testIsAnagramOfReturnsTrue1"
+        val string2 = "testisAnagramOfreturnstrue1"
+
+        assert(string1.isAnagramOf(string2, ignoreWhitespace = true, ignoreCase = false).not())
+    }
+
+    @Test
+    fun `test isAnagramOf ignoreWhitespace False ignoreCase False returns False`() {
+        val string1 = "testisanagramofreturnstrue"
+        val string2 = "testisanagramofreturnstrup"
+
+        assert(string1.isAnagramOf(string2, ignoreWhitespace = false, ignoreCase = false).not())
+    }
+}