If you're in a computer science background, widening your technical horizons is the best thing you should do. However, your programming skills matter the most. And one must continuously keep sharpening these skills, to become a better programmer in the future. Though there are multiple things to focus on, one specific area you must focus on is the world of data structures. Data structures in general are particular approaches to solve problems so that computer resources get used minimum. In general, there are multiple data structures you can learn and implement as well. However, we've covered some basic data structures before, so, now we'll move towards some advanced data structures. Hence, today we're going to learn how to Implement Heap Sort using Java.

 

What is Heap Sort?

 

  • It is a comparison-based sorting algorithm that works on the principles of Binary Heap data structure.

 

  • The algorithm creates a heap of input elements similar to that of binary trees. Elements are divided into sorted and unsorted heaps.

 

  • The largest elements are moved from the unsorted heap to the sorted heap. So the smallest element is kept at the top.

 

  • And this process is repeated further till the entire heap gets sorted.

 

Also Read: Implement Bubble Sort using Java

 

What's The Approach?

 

  • Firstly we'll divide our input array into two parts i.e, inside the heapify() function.

 

  • While doing so, we are going to start from the middle of the input array, and with each iteration, we're going to decrement the index i by one.

 

  • While creating heaps, we'll make sure to keep the largest element as the root (head element).

 

  • The above two instructions will continue to execute till we reach the starting index of the array.

 

  • At the end of the heapify() function, use recursion to sort the sub-heaps as well.

 

Java Program To Implement Heap Sort

 

INPUT:

12, 11, 13, 5, 6, 7

 

OUTPUT:

Sorted array is   5 6 7 11 12 13

 

// 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 code      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);      }  }