Heap Sort Algorithm in JAVA

Heap sort is a comparison-based sorting technique based on Binary Heap data structure. It is similar to selection sort where we first find the minimum element and place the minimum element at the beginning. We repeat the same process for the remaining elements.

Heap Sort Algorithm for sorting in increasing order:

1. Build a max heap from the input data.

2. At this point, the largest item is stored at the root of the heap. Replace it with the last item of the heap followed by reducing the size of heap by 1. Finally, heapify the root of the tree.

3. Repeat step 2 while the size of the heap is greater than 1.

How to build the heap?

Heapify procedure can be applied to a node only if its children nodes are heapified. So the heapification must be performed in the bottom-up order.

Lets understand with the help of an example:

Input data: 4, 10, 3, 5, 1

4(0)

/ \

10(1) 3(2)

/ \

5(3) 1(4)

The numbers in bracket represent the indices in the array

representation of data.

Applying heapify procedure to index 1:

4(0)

/ \

10(1) 3(2)

/ \

5(3) 1(4)

Applying heapify procedure to index 0:

10(0)

/ \

5(1) 3(2)

/ \

4(3) 1(4)

The heapify procedure calls itself recursively to build heap

in top down manner.

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Source Code:-

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package main.algorithm;

public class HeapSort {
    public static 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
    static 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();
    }

    // Main Method
    public static void main(String args[])
    {
        int arr[] = { 8, 3, 18, 27, 16, 7 };
        int n = arr.length;
         sort(arr);

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

Output: Sorted array is
3 7 8 16 18 27

ByteStream

Heap Sort Algorithm in JAVA - Java Tips & Crack