Added Hit Counter in Kotlin

Programming/Kotlin/DesignHitCounter/DesignHitCounter.kt

@@ -0,0 +1,23 @@
+package com.example.testapp
+
+fun main(){
+    //Making an input as the question suggests doesn't really make any sense.
+    val hitCounter = HitCounter()
+    hitCounter.hit(1)
+    hitCounter.hit(2)
+    hitCounter.hit(3)
+    println(hitCounter.getHits(4))
+    hitCounter.hit(300)
+    println(hitCounter.getHits(300))
+    println(hitCounter.getHits(301))
+}
+
+class HitCounter {
+    private val hits = arrayListOf<Int>()
+
+    fun hit(timestamp: Int) = hits.add(timestamp)
+
+    fun getHits(timestamp: Int) : Int = hits.count {
+        it in (timestamp - 300 + 1)..timestamp
+    }
+}