Heap sort is a comparison-based sorting technique based on the Binary Heap data structure. It is similar to the selection sort where first find the maximum element and place it at the end. We repeat the same process for the remaining element.
Heap Sort in Java
Below is the implementation of Heap Sort in Java:
Java
// Java program for implementation of Heap Sort public class HeapSort {
public void sort( int arr[])
{
int n = arr.length;
// Build heap (rearrange array)
for ( int i = n / 2 - 1 ; i >= 0 ; i--)
heapify(arr, n, i);
// One by one extract an element from heap
for ( int i = n - 1 ; i >= 0 ; i--) {
// Move current root to end
int temp = arr[ 0 ];
arr[ 0 ] = arr[i];
arr[i] = temp;
// call max heapify on the reduced heap
heapify(arr, i, 0 );
}
}
// To heapify a subtree rooted with node i which is
// an index in arr[]. n is size of heap
void heapify( int arr[], int n, int i)
{
int largest = i; // Initialize largest as root
int l = 2 * i + 1 ; // left = 2*i + 1
int r = 2 * i + 2 ; // right = 2*i + 2
// If left child is larger than root
if (l < n && arr[l] > arr[largest])
largest = l;
// If right child is larger than largest so far
if (r < n && arr[r] > arr[largest])
largest = r;
// If largest is not root
if (largest != i) {
int swap = arr[i];
arr[i] = arr[largest];
arr[largest] = swap;
// Recursively heapify the affected sub-tree
heapify(arr, n, largest);
}
}
/* A utility function to print array of size n */
static void printArray( int arr[])
{
int n = arr.length;
for ( int i = 0 ; i < n; ++i)
System.out.print(arr[i] + " " );
System.out.println();
}
// Driver program
public static void main(String args[])
{
int arr[] = { 12 , 11 , 13 , 5 , 6 , 7 };
int n = arr.length;
HeapSort ob = new HeapSort();
ob.sort(arr);
System.out.println( "Sorted array is" );
printArray(arr);
}
} |
Complexity of the above program:
Time Complexity : O(N log N), here N is number of elements in array.
Auxiliary Space : O(1), since no extra space used.
Heap Sort Using Java Collection
Steps:
- Convert the input array into a max heap using the priority queue.
- Remove the top element of the max heap and place it at the end of the array.
- Repeat step 2 for all the remaining elements in a heap.
Java
import java.util.*;
public class HeapSortUsingSTL {
// Function to perform the heap sort
public static void heapSort( int [] arr)
{
PriorityQueue<Integer> maxHeap
= new PriorityQueue<>(
Collections.reverseOrder());
for ( int i = 0 ; i < arr.length; i++) {
maxHeap.offer(arr[i]);
}
for ( int i = arr.length - 1 ; i >= 0 ; i--) {
arr[i] = maxHeap.poll();
}
}
// Driver Code
public static void main(String[] args)
{
int [] arr = { 60 , 20 , 40 , 70 , 30 , 10 };
System.out.println( "Before Sorting: "
+ Arrays.toString(arr));
heapSort(arr);
System.out.println( "After Sorting: "
+ Arrays.toString(arr));
}
} |
Output
Before Sorting: [60, 20, 40, 70, 30, 10] After Sorting: [10, 20, 30, 40, 60, 70]
Complexity of the above program:
Time Complexity: O(n log n)
Auxiliary Space: O(n)