Add example for counting sort

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;
+}