Add heapsort algoritham.

Sorting algorithms/Heapsort.java

@@ -0,0 +1,63 @@
+import java.util.*;
+
+public class Heapsort {
+
+   public static void buildheap(int []arr) {
+
+    for(int i=(arr.length-1)/2; i>=0; i--){
+     heapify(arr,i,arr.length-1);
+      }
+   }
+
+   public static void heapify(int[] arr, int i,int size) { 
+      int left = 2*i+1;
+      int right = 2*i+2;
+      int max;
+      if(left <= size && arr[left] > arr[i]){
+       max=left;
+      } else {
+       max=i;
+      }
+
+      if(right <= size && arr[right] > arr[max]) {
+       max=right;
+      }
+      // If max is not current node, exchange it with max of left and right child
+      if(max!=i) {
+         exchange(arr,i, max);
+         heapify(arr, max,size);
+      }
+   }
+
+   public static void exchange(int[] arr,int i, int j) {
+        int t = arr[i];
+        arr[i] = arr[j];
+        arr[j] = t; 
+   }
+
+   public static int[] heapSort(int[] arr) {
+
+      buildheap(arr);
+      int sizeOfHeap=arr.length-1;
+      for(int i=sizeOfHeap; i>0; i--) {
+         exchange(arr,0, i);
+         sizeOfHeap=sizeOfHeap-1;
+         heapify(arr, 0,sizeOfHeap);
+      }
+      return arr;
+   }
+
+   public static void main(String[] args) {
+
+        Scanner s = new Scanner (System.in);
+        System.out.println("Enter number of elements");
+        int n = s.nextInt();
+        int a[] = new int[n];
+        for (int i=0;i<n;i++) {
+            a[i] = s.nextInt();
+        }
+      a=heapSort(a);
+      System.out.println("After Heap Sort : ");
+      System.out.println(Arrays.toString(a));
+   }
+}