Add example for heap sort

This commit is contained in:
Shaun Reed 2021-05-25 18:40:40 -04:00
parent 2f94a59567
commit ef5f952519
5 changed files with 156 additions and 0 deletions

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@ -19,3 +19,4 @@ add_subdirectory(merge)
add_subdirectory(selection) add_subdirectory(selection)
add_subdirectory(insertion) add_subdirectory(insertion)
add_subdirectory(bubble) add_subdirectory(bubble)
add_subdirectory(heap)

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@ -0,0 +1,17 @@
###############################################################################
## Author: Shaun Reed ##
## Legal: All Content (c) 2021 Shaun Reed, all rights reserved ##
## About: A basic CMakeLists configuration to practice heap sort ##
## ##
## Contact: shaunrd0@gmail.com | URL: www.shaunreed.com | GitHub: shaunrd0 ##
###############################################################################
cmake_minimum_required(VERSION 3.16)
project(HeapSort LANGUAGES CXX)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
add_executable(heap-sort "heap-sort.cpp")
add_library(lib-heap "lib-heap.cpp")
target_link_libraries(heap-sort lib-heap)

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@ -0,0 +1,39 @@
/*#############################################################################
## Author: Shaun Reed ##
## Legal: All Content (c) 2021 Shaun Reed, all rights reserved ##
## About: An example implementation of heap sort using a custom library ##
## ##
## Contact: shaunrd0@gmail.com | URL: www.shaunreed.com | GitHub: shaunrd0 ##
###############################################################################
*/
#include "lib-heap.hpp"
#include <algorithm>
#include <vector>
#include <random>
#include <iostream>
int main(const int argc, const char * argv[])
{
srand(time(nullptr));
std::vector<int> array(ARRAY_LENGTH);
// array[0] = 0; // Don't use the 0 index
std::generate(array.begin(), array.end(), [](){ return rand() % 1000;});
auto print = [](std::vector<int> array) {
for (const auto &i : array) {
std::cout << i << ", ";
}
std::cout << std::endl;
};
std::cout << "Unsorted array: \n";
print(array);
// Builds a max heap from the array, and then sorts using HeapSort
HeapSort(array);
std::cout << "Sorted array: \n";
print(array);
}

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@ -0,0 +1,72 @@
/*#############################################################################
## Author: Shaun Reed ##
## Legal: All Content (c) 2021 Shaun Reed, all rights reserved ##
## About: An example implementation of heap sort using a custom library ##
## ##
## Contact: shaunrd0@gmail.com | URL: www.shaunreed.com | GitHub: shaunrd0 ##
###############################################################################
*/
#include "lib-heap.hpp"
#include <algorithm>
#include <vector>
// Parent is unused, but included for completeness
size_t Parent(const size_t &index) { return index / 2;}
size_t Left(const size_t &index) { return 2 * index + 1;}
size_t Right(const size_t &index) { return (2 * index) + 2;}
void MaxHeapify(std::vector<int> &array, size_t thisIndex, int &heapSize)
{
// Get an index for the left and right nodes attached to thisIndex
size_t l = Left(thisIndex);
size_t r = Right(thisIndex);
// Assume thisIndex holds the largest value until proven otherwise
size_t largest = thisIndex;
// For both conditions, make sure l and r are within the heaps size
// If either index l or r hold values that are larger than that of thisIndex
// + Update the largest index
if (l < heapSize && array[l] > array[thisIndex]) {
largest = l;
}
if (r < heapSize && array[r] > array[largest]) {
largest = r;
}
// If l or r contain any value larger than that of thisIndex
if (largest != thisIndex) {
// Swap their values
std::swap(array[thisIndex], array[largest]);
// Run MaxHeapify on the array, using the largest index as thisIndex
MaxHeapify(array, largest, heapSize);
}
}
void BuildMaxHeap(std::vector<int> &array, int &heapSize)
{
// For each value within the heap, starting at last index moving to the first
for (int i = (array.size() / 2); i >= 0; i--) {
// Call MaxHeapify, sorting the value held at index i
MaxHeapify(array, i, heapSize);
}
}
void HeapSort(std::vector<int> &array)
{
// Track the size of the heap
// + Since HeapSort will remain on the call stack until all recursion returns
// + Pass this value by reference to track size of heap as modifiable value
int heapSize = array.size();
// Create a maximum heap from the array using its size
BuildMaxHeap(array, heapSize);
// For each value within the max heap, starting from its final value
for (int i = array.size() - 1; i > 0; i--) {
// Swap the top value within the heap with the value at i
std::swap(array[0], array[i]);
//
heapSize--;
MaxHeapify(array, 0, heapSize);
}
}

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@ -0,0 +1,27 @@
/*#############################################################################
## Author: Shaun Reed ##
## Legal: All Content (c) 2021 Shaun Reed, all rights reserved ##
## About: An example implementation of heap sort using a custom library ##
## ##
## Contact: shaunrd0@gmail.com | URL: www.shaunreed.com | GitHub: shaunrd0 ##
###############################################################################
*/
#ifndef LIB_HEAP_HPP
#define LIB_HEAP_HPP
#include <vector>
#define ARRAY_LENGTH 10
size_t Parent(const size_t &index);
size_t Left(const size_t &index);
size_t Right(const size_t &index);
void MaxHeapify(std::vector<int> &array, size_t thisIndex, int &heapSize);
void BuildMaxHeap(std::vector<int> &array, int &heapSize);
void HeapSort(std::vector<int> &array);
#endif // LIB_HEAP_HPP