From 198fcbf0513c687b36bd6a84d7ecfbd0ee92ae36 Mon Sep 17 00:00:00 2001
From: wgroeneveld <wouter.groeneveld@gmail.com>
Date: Fri, 23 Mar 2018 15:29:08 +0100
Subject: [PATCH] heap sorting

---
 .../src/be/brainbaking/sorting/HeapSort.java  | 90 +++++++++++++++++++
 .../test/be/brainbaking/sorting/SortTest.java | 26 ++++++
 2 files changed, 116 insertions(+)
 create mode 100644 sorting/java/src/be/brainbaking/sorting/HeapSort.java

diff --git a/sorting/java/src/be/brainbaking/sorting/HeapSort.java b/sorting/java/src/be/brainbaking/sorting/HeapSort.java
new file mode 100644
index 0000000..bc2fe43
--- /dev/null
+++ b/sorting/java/src/be/brainbaking/sorting/HeapSort.java
@@ -0,0 +1,90 @@
+package be.brainbaking.sorting;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class HeapSort implements Sortable {
+
+    private String asString(List<Integer> list) {
+        return list.stream().map(i -> i.toString()).collect(Collectors.joining(", "));
+    }
+
+    /**
+     * heap-size[A] <- length[A]
+     * for i <- |length[A]/2| downto 1
+     *   do MAX-HEAPIFY(A, i)
+     */
+    protected List<Integer> buildMaxHeap(List<Integer> list) {
+        System.out.println("to maxify: " + asString(list));
+        List<Integer> heapList = new ArrayList<>(list);
+        int halfIndex = (int)Math.floor(list.size() / 2);
+
+        for(int i =  halfIndex; i >= 1; i--) {
+            maxHeapify(heapList, i);
+        }
+
+        System.out.println("maxified: " + asString(heapList));
+        return heapList;
+    }
+
+    private int leftIndex(int index) {
+        return index * 2;
+    }
+
+    private int rightIndex(int index) {
+        return leftIndex(index) + 1;
+    }
+
+    private int parentIndex(int index) {
+        return (int)Math.floor(index / 2);
+    }
+
+    private void maxHeapify(List<Integer> list, int oneBasedIndex) {
+        int lefti = leftIndex(oneBasedIndex);
+        int righti = rightIndex(oneBasedIndex);
+        int largesti = oneBasedIndex;
+
+        if(lefti <= list.size() && list.get(lefti - 1) > list.get(oneBasedIndex - 1)) {
+            largesti = lefti;
+        }
+        if(righti <= list.size() && list.get(righti - 1) > list.get(largesti - 1)) {
+            largesti = righti;
+        }
+
+        if(largesti != oneBasedIndex) {
+            swap(list, oneBasedIndex, largesti);
+            maxHeapify(list, largesti);
+        }
+    }
+
+    private void swap(List<Integer> list, int oneBasedA, int oneBasedB) {
+        int temp = list.get(oneBasedA - 1);
+        list.set(oneBasedA - 1, list.get(oneBasedB - 1));
+        list.set(oneBasedB - 1, temp);
+    }
+
+    /**
+     * BUILD-MAX-HEAP(A)
+     * for i <- length[A] downto 2
+     *   do exchange A[1] with A[i]
+     *   heap-size[A] <- heap-size[A] - 1
+     *   MAX-HEAPIFY(A, 1)
+     */
+    @Override
+    public List<Integer> sort(List<Integer> list) {
+        List<Integer> heap = buildMaxHeap(list);
+        List<Integer> sorted = new ArrayList<>();
+
+        for(int i = heap.size(); i >= 1; i--) {
+            // in plaats van te swappen met 1, i pitsen we het hoofd van de tree er af
+            // ik wil niet heap-size manipuleren en doorgeven
+            sorted.add(0, heap.get(0));
+            heap.remove(0);
+            maxHeapify(heap, 1);
+        }
+
+        System.out.println("sorted: " + asString(sorted));
+        return sorted;
+    }
+}
diff --git a/sorting/java/test/be/brainbaking/sorting/SortTest.java b/sorting/java/test/be/brainbaking/sorting/SortTest.java
index d5920e1..9a5d094 100644
--- a/sorting/java/test/be/brainbaking/sorting/SortTest.java
+++ b/sorting/java/test/be/brainbaking/sorting/SortTest.java
@@ -4,11 +4,37 @@ import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 
 public class SortTest {
 
+    @Test
+    public void heapSort_withBiggerHeap() {
+        HeapSort sort = new HeapSort();
+
+        List<Integer> expetedSort = Arrays.asList(1, 2, 3, 4, 7, 8, 9, 10, 14, 16);
+        List<Integer> actualSort = sort.sort(Arrays.asList(4, 1, 3, 2, 16, 9, 10, 14, 8, 7));
+
+        Assertions.assertArrayEquals(expetedSort.toArray(), actualSort.toArray());
+    }
+
+    @Test
+    public void heapSort_buildMaxHeap() {
+        HeapSort sort = new HeapSort();
+
+        List<Integer> expectedHeap = Arrays.asList(16, 14, 10, 8, 7, 9, 3, 2, 4, 1);
+        List<Integer> maxHeap = sort.buildMaxHeap(Arrays.asList(4, 1, 3, 2, 16, 9, 10, 14, 8, 7));
+
+        Assertions.assertArrayEquals(expectedHeap.toArray(), maxHeap.toArray());
+    }
+
+    @Test
+    public void heapSort() {
+        simpleTestCaseFor(new HeapSort());
+    }
+
     @Test
     public void insertionSort() {
         simpleTestCaseFor(new InsertionSort());