# C++ Program for Heap Sort

• Difficulty Level : Hard
• Last Updated : 20 Jun, 2022

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

Implementation:

## CPP

 `// 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` `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) { ` `        ``swap(arr[i], arr[largest]); `   `        ``// Recursively heapify the affected sub-tree ` `        ``heapify(arr, n, largest); ` `    ``} ` `} `   `// 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, arr[i]); `   `        ``// call max 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[] = { 12, 11, 13, 5, 6, 7 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr); `   `    ``heapSort(arr, n); `   `    ``cout << ``"Sorted array is \n"``; ` `    ``printArray(arr, n); ` `} `

Output:

```Sorted array is
5 6 7 11 12 13```

Time complexity : O(N*logN)
Auxiliary space: O(1)

Please refer complete article on Heap Sort for more details!

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