impl top K items

scala/src/main/scala/ch29_heap_solutions/TopKItemsKeeper.scala

@@ -0,0 +1,30 @@
+package ch29_heap_solutions
+
+import scala.collection.mutable
+
+/**
+  * keep the top k items in the the class
+  */
+class TopKItemsKeeper(val itemsToKeepCount: Int) {
+
+
+  //have a smallest value top heap
+  val queue = new mutable.PriorityQueue[Int]()(scala.math.Ordering.Int.reverse)
+
+  def put(item: Int): Unit = {
+    if (queue.length < itemsToKeepCount) {
+      queue += item
+      return
+    }
+
+    //queue already have the k items
+    if (item.compareTo(queue.head) > 0) {
+      queue.dequeue()
+      queue += item
+    }
+  }
+
+  def get(): List[Int] = {
+    queue.clone().dequeueAll
+  }
+}

scala/src/test/scala/ch29_heap_solutions/TopKItemsKeeperTest.scala

@@ -0,0 +1,25 @@
+package ch29_heap_solutions
+
+import org.scalatest.{FlatSpec, Matchers}
+
+import scala.util.Random
+
+class TopKItemsKeeperTest extends FlatSpec with Matchers {
+
+  behavior of "TopKItemsKeeperTest"
+
+  it should "put and get top K from the keeper" in {
+    val length = 50
+    val k = 5
+    val topKItemsKeeper = new TopKItemsKeeper(k)
+    val nums = new Array[Int](length)
+    for (i <- Range(0, length)) {
+      nums(i) = Random.nextInt
+    }
+
+    nums.foreach(topKItemsKeeper.put)
+    val ordering = scala.math.Ordering.Int.reverse
+    topKItemsKeeper.get().toArray.sorted(ordering) should equal(nums.sorted(ordering).slice(0, k))
+  }
+
+}