impl heap sort

Author: email2liyang

scala/src/main/scala/ch28_heap/Heap.scala

@@ -4,6 +4,22 @@ import scala.util.control.Breaks._
 
 class Heap(val capacity: Int, var elementCount: Int = 0) {
 
+  def this(arrayParam: Array[Int], bottomUp: Boolean) = {
+    this(arrayParam.length + 1)
+    if (bottomUp) {
+      arrayParam.foreach(this.insert)
+    } else {
+      //copy data into array of heap
+      for (i <- arrayParam.indices) {
+        array(i + 1) = arrayParam(i)
+        elementCount = arrayParam.length
+      }
+      for (i <- elementCount / 2 + 1 to 1 by -1) {
+        heapifyTopDown(i, elementCount - 1)
+      }
+    }
+  }
+
   require(capacity > 0, "capacity should be > 0")
   val array: Array[Int] = new Array[Int](capacity)
 
@@ -41,7 +57,7 @@ class Heap(val capacity: Int, var elementCount: Int = 0) {
   //start from the top to compare with it's child nodes
   //swap if child node > parent node
   //stop at child node <= parent node
-  private[this] def  heapifyTopDown(startIndex: Int, stopIndex: Int) = {
+  private[this] def heapifyTopDown(startIndex: Int, stopIndex: Int) = {
     var pointer = startIndex
     breakable {
       while (true) {
@@ -66,3 +82,14 @@ class Heap(val capacity: Int, var elementCount: Int = 0) {
   }
 
 }
+
+object Heap {
+  def heapSort(array: Array[Int]): Array[Int] = {
+    val result = new Array[Int](array.length)
+    val heap = new Heap(array, true)
+    for (i <- result.length - 1 to 0 by -1) {
+      result(i) = heap.removeMax()
+    }
+    result
+  }
+}

scala/src/test/scala/ch11_sorts/SortsTest.scala

@@ -1,6 +1,7 @@
 package ch11_sorts
 
 import ch12_sorts.{MergeSort, QuickSort}
+import ch28_heap.Heap
 import org.scalatest.{FlatSpec, Matchers}
 
 import scala.util.Random
@@ -53,6 +54,7 @@ class SortsTest extends FlatSpec with Matchers {
     timed("selectionSort", Sorts.selectionSort, array.clone())
     timed("mergeSort", MergeSort.mergeSort, array.clone())
     timed("quickSort", QuickSort.quickSort, array.clone())
+    timed("heapSort", Heap.heapSort, array.clone())
   }
 
   def reportElapsed(name: String, time: Long): Unit = println(name + " takes in " + time + "ms")

scala/src/test/scala/ch28_heap/HeapTest.scala

@@ -15,4 +15,29 @@ class HeapTest extends FlatSpec with Matchers {
     heap.removeMax() should equal(27)
   }
 
+  it should "build heap from array - bottom up" in {
+    val nums = Array(33, 27, 21, 16, 13, 15, 19, 5, 6, 7, 8, 1, 2, 12)
+    val heap = new Heap(nums, true)
+
+    heap.removeMax() should equal(33)
+    heap.removeMax() should equal(27)
+  }
+
+  it should "build heap from array - top down" in {
+    val nums = Array(33, 27, 21, 16, 13, 15, 19, 5, 6, 7, 8, 1, 2, 12)
+    val heap = new Heap(nums, false)
+
+    heap.removeMax() should equal(33)
+    heap.removeMax() should equal(27)
+  }
+
+  it should "sort array" in {
+    it should "build heap from array - top down" in {
+      val nums = Array(33, 27, 21, 16, 13, 15, 19, 5, 6, 7, 8, 1, 2, 12)
+      val result = Heap.heapSort(nums)
+
+      result.mkString("") should equal(nums.sorted.mkString(""))
+    }
+  }
+
 }