Add Duplicate Character Counter in Kotlin (#5050)

* Implemented duplicate character counter

* Added missing output message

Author: jrg94

archive/k/kotlin/DuplicateCharacterCounter.kt

@@ -0,0 +1,34 @@
+import kotlin.system.exitProcess
+
+fun main(args: Array<String>) {
+    val phrase: String = errorChecking(args)
+    val counts = duplicateCharacterCount(phrase)
+    outputMap(counts)
+}
+
+fun usageError() {
+    println("Usage: please provide a string")
+}
+
+fun errorChecking(args: Array<String>): String {
+    if (args.size == 0 || args[0] == "") {
+       usageError()
+       exitProcess(1)
+    }
+    return args[0]
+}
+
+fun duplicateCharacterCount(phrase: String): Map<Char, Int> {
+    val counts: Map<Char, Int> = phrase.groupingBy { it }.eachCount()
+    return counts.filter { it.value > 1 }
+}
+
+fun outputMap(counts: Map<Char, Int>) {
+    if (counts.size > 0) {
+        for (pair in counts) {
+            println("${pair.key}: ${pair.value}")
+        }
+    } else {
+        println("No duplicate characters")
+    }
+}