Java Program for Heap Sort

Last Updated : 10 Jan, 2024

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)

Please refer complete article on Heap Sort for more details!

C++ Program for Heap Sort

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Java Program for Heap Sort

Heap Sort in Java

Complexity of the above program:

Heap Sort Using Java Collection

Complexity of the above program:

Please refer complete article on Heap Sort for more details!

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