Add example for counting sort

cpp/algorithms/sorting/CMakeLists.txt

@@ -21,3 +21,4 @@ add_subdirectory(insertion)
 add_subdirectory(bubble)
 add_subdirectory(heap)
 add_subdirectory(quick)
+add_subdirectory(count)

cpp/algorithms/sorting/count/CMakeLists.txt

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

cpp/algorithms/sorting/count/counting-sort.cpp

@@ -0,0 +1,40 @@
+/*#############################################################################
+## Author: Shaun Reed                                                        ##
+## Legal: All Content (c) 2021 Shaun Reed, all rights reserved               ##
+## About: An example implementation of counting sort using a custom library  ##
+##                                                                           ##
+## Contact: shaunrd0@gmail.com  | URL: www.shaunreed.com | GitHub: shaunrd0  ##
+###############################################################################
+*/
+
+#include "lib-counting.hpp"
+
+#include <algorithm>
+#include <iostream>
+#include <random>
+#include <vector>
+
+
+int main(const int argc, const char * argv[])
+{
+  srand(time(nullptr));
+  std::vector<int> array(ARRAY_LENGTH);
+  // For this example, we limit the maximum value to 10
+  // + This helps to provide duplicates so we have > 1 count of some values
+  std::generate(array.begin(), array.end(), [](){ return rand() % 10;});
+
+  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);
+
+  CountingSort(array);
+
+  std::cout << "Sorted array: \n";
+  print(array);
+}

cpp/algorithms/sorting/count/lib-counting.cpp

@@ -0,0 +1,49 @@
+/*#############################################################################
+## Author: Shaun Reed                                                        ##
+## Legal: All Content (c) 2021 Shaun Reed, all rights reserved               ##
+## About: An example implementation of counting sort using a custom library  ##
+##                                                                           ##
+## Contact: shaunrd0@gmail.com  | URL: www.shaunreed.com | GitHub: shaunrd0  ##
+###############################################################################
+*/
+
+#include "lib-counting.hpp"
+
+#include <algorithm>
+#include <cstdint>
+#include <vector>
+
+
+void CountingSort(std::vector<int> &array)
+{
+  std::vector<int> sortedArray(ARRAY_LENGTH);
+  // Find the maximum value within the array to sort
+  int32_t maxValue = INT32_MIN;
+  for (const auto &val : array) maxValue = (val > maxValue) ? val : maxValue;
+
+  // Create an array with element for all *values* within the range of the set
+  // + Not the size of the array to sort, but instead a element of
+  // + tempArray[val] = 0; for each val within the array we want to sort
+  // Add one to maxValue to make up for zero index; 0's are possible, too!
+  std::vector<int> tempArray(maxValue + 1, 0);
+
+  // Count the occurrences of each value within the array to sort
+  // + Store the end result as tempArray[value] = count;
+  for (const auto &val : array) tempArray[val] += 1;
+
+  // Count the values less than or equal to each element of tempArray
+  // + Since each element stores its own count, just add the count at index i-1
+  for (size_t i = 1; i <= maxValue; i++) {
+    tempArray[i] += tempArray[i - 1];
+  }
+
+  for (ssize_t arrayIndex = array.size() - 1; arrayIndex >= 0; arrayIndex--) {
+    // Store as references; Changes reflect on actual values within each array
+    const int &arrayValue = array[arrayIndex];
+    int &valueCount = tempArray[arrayValue];
+    sortedArray[valueCount - 1] = arrayValue;
+    valueCount = valueCount - 1;
+  }
+
+  array = sortedArray;
+}

cpp/algorithms/sorting/count/lib-counting.hpp

@@ -0,0 +1,21 @@
+/*#############################################################################
+## Author: Shaun Reed                                                        ##
+## Legal: All Content (c) 2021 Shaun Reed, all rights reserved               ##
+## About: An example implementation of counting sort using a custom library  ##
+##                                                                           ##
+## Contact: shaunrd0@gmail.com  | URL: www.shaunreed.com | GitHub: shaunrd0  ##
+###############################################################################
+*/
+
+#ifndef LIB_COUNT_HPP
+#define LIB_COUNT_HPP
+
+#include <vector>
+
+// For this example double the size of the array so we have more values to count
+#define ARRAY_LENGTH 20
+
+
+void CountingSort(std::vector<int> &array);
+
+#endif // LIB_COUNT_HPP