From ab9f58704c883e28fe1567cc55d52fe80d9a016f Mon Sep 17 00:00:00 2001
From: Ivan Li <email2liyang@gmail.com>
Date: Thu, 10 Jan 2019 13:35:55 +0800
Subject: [PATCH] impl top K items

---
 .../ch29_heap_solutions/TopKItemsKeeper.scala | 30 +++++++++++++++++++
 .../TopKItemsKeeperTest.scala                 | 25 ++++++++++++++++
 2 files changed, 55 insertions(+)
 create mode 100644 scala/src/main/scala/ch29_heap_solutions/TopKItemsKeeper.scala
 create mode 100644 scala/src/test/scala/ch29_heap_solutions/TopKItemsKeeperTest.scala

diff --git a/scala/src/main/scala/ch29_heap_solutions/TopKItemsKeeper.scala b/scala/src/main/scala/ch29_heap_solutions/TopKItemsKeeper.scala
new file mode 100644
index 0000000..88eba56
--- /dev/null
+++ b/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
+  }
+}
diff --git a/scala/src/test/scala/ch29_heap_solutions/TopKItemsKeeperTest.scala b/scala/src/test/scala/ch29_heap_solutions/TopKItemsKeeperTest.scala
new file mode 100644
index 0000000..b3dd0c9
--- /dev/null
+++ b/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))
+  }
+
+}