heapsort.java

import java.util.*;
public class HeapSort {
		public void sort(int arr[])
		{
			int N = arr.length;

			for (int i = N / 2 - 1; i >= 0; i--)
				heapify(arr, N, i);

			for (int i = N - 1; i > 0; i--) {

				int x = arr[0];
				arr[0] = arr[i];
				arr[i] = x;

				heapify(arr, i, 0);
			}
		}

		void heapify(int arr[], int N, int i)
		{
			int largest = i; 
			int l = 2 * i + 1; 
			int r = 2 * i + 2; 

			if (l < N && arr[l] > arr[largest])
				largest = l;

			if (r < N && arr[r] > arr[largest])
				largest = r;

			if (largest != i) {
				int swap = arr[i];
				arr[i] = arr[largest];
				arr[largest] = swap;

				heapify(arr, N, largest);
			}
		}
		static void printArray(int arr[])
		{
			int N = arr.length;

			for (int i = 0; i < N; ++i)
				System.out.print(arr[i] + " ");
			System.out.println();
		}

		public static void main(String args[])
		{
			 int i, n, arr[];

		      Scanner s = new Scanner(System.in);
		      System.out.println("Enter no. of elements in aray:");
		      n = s.nextInt(); 

		      arr = new int[n];

		      System.out.println("Enter " + n + " integers:");

		      for (i = 0;i<n; i++)
		          arr[i] = s.nextInt();

			HeapSort ob = new HeapSort();
			ob.sort(arr);

			System.out.println("Sorted array is");
			printArray(arr);
		}
	

}