/** * \addtogroup sorting Sorting Algorithm * @{ * \file * \brief [Heap Sort Algorithm * (HEAP SORT)](https://en.wikipedia.org/wiki/Heapsort) implementation * * \author [Ayaan Khan](http://github.com/ayaankhan98) * * \details * heapsort is a comparison-based sorting algorithm. * Heapsort can be thought of as an improved selection sort: * like selection sort, heapsort divides its input into a sorted * and an unsorted region, and it iteratively shrinks the unsorted * region by extracting the largest element from it and inserting * it into the sorted region. Unlike selection sort, * heapsort does not waste time with a linear-time scan of the * unsorted region; rather, heap sort maintains the unsorted region * in a heap data structure to more quickly find the largest element * in each step. * * Time Complexity - O(nlog(n)) * */ #include /** * * Utility Lambda function to print the array after * sorting. * * @param arr array to be printed * @param sz size of array * */ auto printArray = [](int *arr, int sz) { for (int i = 0; i < sz; i++) std::cout << arr[i] << " "; std::cout << "\n"; }; /** * * The heapify procedure can be thought of as building a heap from * the bottom up by successively sifting downward to establish the * heap property. * * @param arr array be to sorted * @param */ void (*heapify)(int *arr, int n, int i) = [](int *arr, int n, int i) { int largest = i; int l = 2 * i + 1; int r = 2 * i + 2; if (l < n && arr[l] > arr[largest]) largest = l; if (r < n && arr[r] > arr[largest]) largest = r; if (largest != i) { std::swap(arr[i], arr[largest]); heapify(arr, n, largest); } }; /** * heapSort lambda function utilizes heapify procedure to sort * the array * * @param arr array to be sorted * @param n size of array * */ auto heapSort = [](int *arr, int n) { for (int i = n - 1; i >= 0; i--) heapify(arr, n, i); for (int i = n - 1; i >= 0; i--) { std::swap(arr[0], arr[i]); heapify(arr, i, 0); } }; /** Main function */ int main() { int arr[] = {-10, 78, -1, -6, 7, 4, 94, 5, 99, 0}; int sz = sizeof(arr) / sizeof(arr[0]); // sz - size of array printArray(arr, sz); // displaying the array before sorting heapSort(arr, sz); // calling heapsort to sort the array printArray(arr, sz); // display array after sorting return 0; } /** @} */