From 9a714d34eab39ff993eee0d25d66e066074e1c67 Mon Sep 17 00:00:00 2001
From: augustoaccorsi <augusto.acorsi@gmail.com>
Date: Sat, 16 Oct 2021 13:11:00 -0300
Subject: [PATCH] add heapsort

---
 java/HeapSort.java | 49 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 java/HeapSort.java

diff --git a/java/HeapSort.java b/java/HeapSort.java
new file mode 100644
index 0000000..5733547
--- /dev/null
+++ b/java/HeapSort.java
@@ -0,0 +1,49 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+class HeapSort {
+    public void sort(List<Integer> list)
+    {
+        for (int i = (list.size()/2 - 1); i >= 0; i--) {
+            heapify(list, list.size(), i);
+        }
+
+        for (int i = list.size() - 1; i > 0; i--) {
+            Collections.swap(list,0,i);
+            heapify(list, i, 0);
+        }
+    }
+
+    void heapify(List<Integer> list, int n, int i)
+    {
+        int largest = i;
+        int l = 2 * i + 1;
+        int r = 2 * i + 2;
+
+        if (l < n && list.get(l) > list.get(largest)) {
+            largest = l;
+        }
+
+        if (r < n && list.get(r) > list.get(largest)){
+            largest = r;
+        }
+
+        if (largest != i) {
+            Collections.swap(list, i, largest);
+            heapify(list, n, largest);
+        }
+    }
+
+    public static void main(String[] args)
+    {
+        List<Integer> list = new ArrayList<>(Arrays.asList(1,2,3,4,5,6,6,7,8,9,10));
+        HeapSort heap = new HeapSort();
+
+        Collections.shuffle(list);
+        System.out.println(list);
+        heap.sort(list);
+        System.out.println(list);
+    }
+}