# Heap Sort for decreasing order using min heap

• Difficulty Level : Easy
• Last Updated : 04 Aug, 2022

Given an array of elements, sort the array in decreasing order using min heap.

Examples:

```Input : arr[] = {5, 3, 10, 1}
Output : arr[] = {10, 5, 3, 1}

Input : arr[] = {1, 50, 100, 25}
Output : arr[] = {100, 50, 25, 1}```

Prerequisite : Heap sort using min heap.

Algorithm :

1. Build a min heap from the input data.
2. At this point, the smallest 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 tree.
3. Repeat above steps while size of heap is greater than 1.

Note :Heap Sort using min heap sorts in descending order where as max heap sorts in ascending order

Implementation:

## C++

 `// C++ program for implementation of Heap Sort``#include ``using` `namespace` `std;` `// 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` `smallest = i; ``// Initialize smallest as root``    ``int` `l = 2 * i + 1; ``// left = 2*i + 1``    ``int` `r = 2 * i + 2; ``// right = 2*i + 2` `    ``// If left child is smaller than root``    ``if` `(l < n && arr[l] < arr[smallest])``        ``smallest = l;` `    ``// If right child is smaller than smallest so far``    ``if` `(r < n && arr[r] < arr[smallest])``        ``smallest = r;` `    ``// If smallest is not root``    ``if` `(smallest != i) {``        ``swap(arr[i], arr[smallest]);` `        ``// Recursively heapify the affected sub-tree``        ``heapify(arr, n, smallest);``    ``}``}` `// main function to do heap sort``void` `heapSort(``int` `arr[], ``int` `n)``{``    ``// 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``        ``swap(arr[0], arr[i]);` `        ``// call min heapify on the reduced heap``        ``heapify(arr, i, 0);``    ``}``}` `/* A utility function to print array of size n */``void` `printArray(``int` `arr[], ``int` `n)``{``    ``for` `(``int` `i = 0; i < n; ++i)``        ``cout << arr[i] << ``" "``;``    ``cout << ``"\n"``;``}` `// Driver program``int` `main()``{``    ``int` `arr[] = { 4, 6, 3, 2, 9 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);` `    ``heapSort(arr, n);` `    ``cout << ``"Sorted array is \n"``;``    ``printArray(arr, n);``}`

## Java

 `// Java program for implementation of Heap Sort` `import` `java.io.*;` `class` `GFG {``    ` `    ``// 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` `smallest = i; ``// Initialize smallest as root``        ``int` `l = ``2` `* i + ``1``; ``// left = 2*i + 1``        ``int` `r = ``2` `* i + ``2``; ``// right = 2*i + 2` `        ``// If left child is smaller than root``        ``if` `(l < n && arr[l] < arr[smallest])``            ``smallest = l;` `        ``// If right child is smaller than smallest so far``        ``if` `(r < n && arr[r] < arr[smallest])``            ``smallest = r;` `        ``// If smallest is not root``        ``if` `(smallest != i) {``            ``int` `temp = arr[i];``            ``arr[i] = arr[smallest];``            ``arr[smallest] = temp;` `            ``// Recursively heapify the affected sub-tree``            ``heapify(arr, n, smallest);``        ``}``    ``}` `    ``// main function to do heap sort``    ``static` `void` `heapSort(``int` `arr[], ``int` `n)``    ``{``        ``// 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 min heapify on the reduced heap``            ``heapify(arr, i, ``0``);``        ``}``    ``}` `    ``/* A utility function to print array of size n */``    ``static` `void` `printArray(``int` `arr[], ``int` `n)``    ``{``        ``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[] = { ``4``, ``6``, ``3``, ``2``, ``9` `};``        ``int` `n = arr.length;` `        ``heapSort(arr, n);` `        ``System.out.println(``"Sorted array is "``);``        ``printArray(arr, n);``    ``}``}` `// This code is contributed by vt_m.`

## Python3

 `# Python3 program for implementation``# of Heap Sort` `# To heapify a subtree rooted with``# node i which is an index in arr[].``# n is size of heap``def` `heapify(arr, n, i):``    ``smallest ``=` `i ``# Initialize smallest as root``    ``l ``=` `2` `*` `i ``+` `1` `# left = 2*i + 1``    ``r ``=` `2` `*` `i ``+` `2` `# right = 2*i + 2` `    ``# If left child is smaller than root``    ``if` `l < n ``and` `arr[l] < arr[smallest]:``        ``smallest ``=` `l` `    ``# If right child is smaller than``    ``# smallest so far``    ``if` `r < n ``and` `arr[r] < arr[smallest]:``        ``smallest ``=` `r` `    ``# If smallest is not root``    ``if` `smallest !``=` `i:``        ``(arr[i],``         ``arr[smallest]) ``=` `(arr[smallest],``                           ``arr[i])` `        ``# Recursively heapify the affected``        ``# sub-tree``        ``heapify(arr, n, smallest)` `# main function to do heap sort``def` `heapSort(arr, n):``    ` `    ``# Build heap (rearrange array)``    ``for` `i ``in` `range``(``int``(n ``/` `2``) ``-` `1``, ``-``1``, ``-``1``):``        ``heapify(arr, n, i)` `    ``# One by one extract an element``    ``# from heap``    ``for` `i ``in` `range``(n``-``1``, ``-``1``, ``-``1``):``        ` `        ``# Move current root to end #``        ``arr[``0``], arr[i] ``=` `arr[i], arr[``0``]` `        ``# call min heapify on the reduced heap``        ``heapify(arr, i, ``0``)` `# A utility function to print``# array of size n``def` `printArray(arr, n):``    ` `    ``for` `i ``in` `range``(n):``        ``print``(arr[i], end ``=` `" "``)``    ``print``()` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``    ``arr ``=` `[``4``, ``6``, ``3``, ``2``, ``9``]``    ``n ``=` `len``(arr)` `    ``heapSort(arr, n)` `    ``print``(``"Sorted array is "``)``    ``printArray(arr, n)` `# This code is contributed by PranchalK`

## C#

 `// C# program for implementation of Heap Sort``using` `System;` `class` `GFG {``    ` `    ``// 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` `smallest = i; ``// Initialize smallest as root``        ``int` `l = 2 * i + 1; ``// left = 2*i + 1``        ``int` `r = 2 * i + 2; ``// right = 2*i + 2` `        ``// If left child is smaller than root``        ``if` `(l < n && arr[l] < arr[smallest])``            ``smallest = l;` `        ``// If right child is smaller than smallest so far``        ``if` `(r < n && arr[r] < arr[smallest])``            ``smallest = r;` `        ``// If smallest is not root``        ``if` `(smallest != i) {``            ``int` `temp = arr[i];``            ``arr[i] = arr[smallest];``            ``arr[smallest] = temp;` `            ``// Recursively heapify the affected sub-tree``            ``heapify(arr, n, smallest);``        ``}``    ``}` `    ``// main function to do heap sort``    ``static` `void` `heapSort(``int``[] arr, ``int` `n)``    ``{``        ``// 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 min heapify on the reduced heap``            ``heapify(arr, i, 0);``        ``}``    ``}` `    ``/* A utility function to print array of size n */``    ``static` `void` `printArray(``int``[] arr, ``int` `n)``    ``{``        ``for` `(``int` `i = 0; i < n; ++i)``            ``Console.Write(arr[i] + ``" "``);``        ``Console.WriteLine();``    ``}` `    ``// Driver program``    ``public` `static` `void` `Main()``    ``{``        ``int``[] arr = { 4, 6, 3, 2, 9 };``        ``int` `n = arr.Length;` `        ``heapSort(arr, n);` `        ``Console.WriteLine(``"Sorted array is "``);``        ``printArray(arr, n);``    ``}``}` `// This code is contributed by vt_m.`

## Javascript

 ``

Output:

```Sorted array is
9 6 4 3 2```

Time complexity:It takes O(logn) for heapify and O(n) for constructing a heap. Hence, the overall time complexity of heap sort using min heap or max heap is O(nlogn)
Space complexity: O(n) for call stack

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