From 66973cf46d7a2c1444001423a87730d29ff576e8 Mon Sep 17 00:00:00 2001
From: Abhinav Sarkar <abhinav@abhinavsarkar.net>
Date: Mon, 8 Jul 2019 18:45:12 +0530
Subject: [PATCH] Adds heap sort

---
 .../algorist/sort/HeapSorter.java             | 69 +++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 src/main/java/net/abhinavsarkar/algorist/sort/HeapSorter.java

diff --git a/src/main/java/net/abhinavsarkar/algorist/sort/HeapSorter.java b/src/main/java/net/abhinavsarkar/algorist/sort/HeapSorter.java
new file mode 100644
index 0000000..8874543
--- /dev/null
+++ b/src/main/java/net/abhinavsarkar/algorist/sort/HeapSorter.java
@@ -0,0 +1,69 @@
+package net.abhinavsarkar.algorist.sort;
+
+import java.util.Arrays;
+import net.abhinavsarkar.algorist.Sorter;
+
+public class HeapSorter<T> implements Sorter<T>
+{
+    @Override
+    public T[] sort(T[] input, Comparator<T> comparator)
+    {
+        if (input.length <= 1) {
+            return input;
+        }
+
+        heapify(input, comparator);
+        deheapify(input, comparator);
+        return input;
+    }
+
+    private void heapify(T[] input, Comparator<T> comparator)
+    {
+        for (int i = (input.length - 1)/2; i >= 0; i--) {
+            bubbleDown(input, i, input.length, comparator);
+        }
+    }
+
+    private void deheapify(T[] input, Comparator<T> comparator)
+    {
+        for (int i = input.length; i > 1; i--) {
+            swap(input, 0, i - 1);
+            bubbleDown(input, 0, i - 1, comparator);
+        }
+    }
+
+    private void bubbleDown(T[] input, int index, int size, Comparator<T> comparator) {
+        int maxIdx = index;
+        maxIdx = getMaxIdx(input, index * 2 + 1, maxIdx, size, comparator);
+        maxIdx = getMaxIdx(input, index * 2 + 2, maxIdx, size, comparator);
+        if (index != maxIdx) {
+            swap(input, index, maxIdx);
+            bubbleDown(input, maxIdx, size, comparator);
+        }
+    }
+
+    private int getMaxIdx(T[] input, int childIndex, int minIndex, int size, Comparator<T> comparator)
+    {
+        return childIndex < size && comparator.compare(input[minIndex], input[childIndex]) < 0 ?
+                childIndex : minIndex;
+    }
+
+    private void swap(T[] input, int i, int j)
+    {
+        if (i == j) {
+            return;
+        }
+        T temp = input[i];
+        input[i] = input[j];
+        input[j] = temp;
+    }
+
+    public static void main(String[] args)
+    {
+        Sorter<String> sorter = new HeapSorter<>();
+        String[] sorted =
+                sorter.sort(new String[]{"abhinav", "sarkar", "barista", "jordan", "zebra", "data"},
+                        (s, anotherString) -> anotherString.compareTo(s));
+        System.out.println(Arrays.toString(sorted));
+    }
+}