diff --git a/sorting/heap_sort.cpp b/sorting/heap_sort.cpp index 9948bb821..ef9f87094 100644 --- a/sorting/heap_sort.cpp +++ b/sorting/heap_sort.cpp @@ -1,52 +1,123 @@ +/** + * \file + * \brief [Heap Sort Algorithm + * (heap sort)](https://en.wikipedia.org/wiki/Heapsort) implementation + * + * \author [Ayaan Khan](http://github.com/ayaankhan98) + * + * \details + * Heap-sort is a comparison-based sorting algorithm. + * Heap-sort can be thought of as an improved selection sort: + * like selection sort, heap sort 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, + * heap sort 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 - \f$O(n \log(n))\f$ + * + */ #include +#include #include -void heapify(int *a, int i, int n) { - int largest = i; - const int l = 2 * i + 1; - const int r = 2 * i + 2; +/** + * + * Utility Lambda function to print the array after + * sorting. + * + * @param arr array to be printed + * @param sz size of array + * + */ +template +void printArray(T *arr, int sz) { + for (int i = 0; i < sz; i++) std::cout << arr[i] << " "; + std::cout << "\n"; +} - if (l < n && a[l] > a[largest]) +/** + * + * \addtogroup sorting Sorting Algorithm + * @{ + * + * 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 to be sorted + * @param n size of array + * @param i node position in Binary Tress or element position in + * Array to be compared with it's childern + * + */ +template +void heapify(T *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 && a[r] > a[largest]) + if (r < n && arr[r] > arr[largest]) largest = r; if (largest != i) { - std::swap(a[i], a[largest]); - heapify(a, n, largest); + std::swap(arr[i], arr[largest]); + heapify(arr, n, largest); } } -void heapsort(int *a, int n) { - for (int i = n - 1; i >= 0; --i) { - std::swap(a[0], a[i]); - heapify(a, 0, i); +/** + * Utilizes heapify procedure to sort + * the array + * + * @param arr array to be sorted + * @param n size of array + * + */ +template +void heapSort(T *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); } } -void build_maxheap(int *a, int n) { - for (int i = n / 2 - 1; i >= 0; --i) { - heapify(a, i, n); - } +/** + * + * @} + * Test cases to test the program + * + */ +void test() { + std::cout << "Test 1\n"; + 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 + assert(std::is_sorted(arr, arr + sz)); + std::cout << "Test 1 Passed\n========================\n"; + + std::cout << "Test 2\n"; + double arr2[] = {4.5, -3.6, 7.6, 0, 12.9}; + sz = sizeof(arr2) / sizeof(arr2[0]); + printArray(arr2, sz); + heapSort(arr2, sz); + printArray(arr2, sz); + assert(std::is_sorted(arr2, arr2 + sz)); + std::cout << "Test 2 passed\n"; } +/** Main function */ int main() { - int n; - std::cout << "Enter number of elements of array\n"; - std::cin >> n; - int a[20]; - for (int i = 0; i < n; ++i) { - std::cout << "Enter Element " << i << std::endl; - std::cin >> a[i]; - } - - build_maxheap(a, n); - heapsort(a, n); - std::cout << "Sorted Output\n"; - for (int i = 0; i < n; ++i) { - std::cout << a[i] << std::endl; - } - - std::getchar(); + test(); + return 0; }