Create heap in java (#189)

Author: kumaraguru16

heap in java

@@ -0,0 +1,63 @@
+public class HeapSort {
+
+    private static int[] array = new int[]{5, 3, 6, 4, 8, 9 , 1, 10};
+
+    public static void main(String[] args) {
+        heapSort();
+
+        for(int i : array) {
+            System.out.println(i);
+        }
+    }
+
+    private static void heapSort() {
+        int length = array.length;
+
+        buildMaxHeap(array, length);
+        for(int i = length - 1; i > 0; i--) {
+            int temp = array[0];
+            array[0] = array[i];
+            array[i] = temp;
+            maxHeapify(array, 1, i);
+        }
+    }
+
+    private static void buildMaxHeap(int[] array, int heapSize) {
+        if(array == null) {
+            throw new NullPointerException("null");
+        }
+        if(array.length <=0 || heapSize <= 0) {
+            throw new IllegalArgumentException("illegal");
+        }
+        if(heapSize > array.length) {
+            heapSize = array.length;
+        }
+
+        for(int i = heapSize/2; i > 0; i--) {
+            maxHeapify(array, i, heapSize);
+        }
+    }
+
+    private static void maxHeapify(int[] array, int index, int heapSize) {
+        int l = index * 2;
+        int r = l + 1;
+        int largest;
+
+        if(l <= heapSize && array[l - 1] > array[index - 1]) {
+            largest = l;
+        } else {
+            largest = index;
+        }
+
+        if(r <= heapSize && array[r - 1] > array[largest - 1]) {
+            largest = r;
+        }
+
+        if(largest != index) {
+            int temp = array[index - 1];
+            array[index - 1] = array[largest - 1];
+            array[largest - 1] = temp;
+            maxHeapify(array, largest, heapSize);
+        }
+    }
+}