From bf271f103d1979ea61ce384d251a6fefe96e3f11 Mon Sep 17 00:00:00 2001
From: seancyw <seancyw@gmail.com>
Date: Tue, 7 Feb 2017 22:07:38 +0800
Subject: [PATCH] Implemented Counting Sort Algorithms

---
 Algorithms/SortAlgorithms.h | 37 +++++++++++++++++++++++++++++
 Algorithms/main.cpp         | 46 +++++++++++++++++++++++++++++++++++--
 2 files changed, 81 insertions(+), 2 deletions(-)

diff --git a/Algorithms/SortAlgorithms.h b/Algorithms/SortAlgorithms.h
index 4ffcefe..b966116 100644
--- a/Algorithms/SortAlgorithms.h
+++ b/Algorithms/SortAlgorithms.h
@@ -147,6 +147,43 @@ namespace sortAlgorithms
 		};
 	}
 
+	template<typename T>
+	void countingSort(std::vector<T> & data, bool ascending)
+	{
+		if (data.size() == 0) {
+			throw std::exception("Nothing to sort!");
+			return;
+		}
+
+		//Get the maximum element in the list as the maximum counter
+		//range
+		int maximumElement = *std::max_element(data.begin(), data.end());
+		std::vector<int> counter(maximumElement + 1);
+		std::fill(counter.begin(), counter.end(), 0);
+
+		//Store count for each element
+		for (int i = 0; i < data.size(); ++i)
+			++counter[data[i]];
+		
+		//Recalculate each counter[i] so that it contains the actual
+		//position of the elements
+		for (int i = 1; i < counter.size(); ++i)
+			counter[i] += counter[i - 1];
+
+		//Initialize a temporary array to store the sorted array
+		std::vector<T> temp( data.size() );
+		for (int i = 0; i < data.size(); ++i) {
+			temp[counter[data[i]] - 1] = data[i];
+			--counter[data[i]];
+		}
+
+		//Copy the sort array back to original array
+		data = temp;
+
+		if (!ascending)
+			std::reverse(data.begin(), data.end());
+	}
+
 	template<typename T>
 	class MergeSort
 	{
diff --git a/Algorithms/main.cpp b/Algorithms/main.cpp
index 254dee3..875f1b7 100644
--- a/Algorithms/main.cpp
+++ b/Algorithms/main.cpp
@@ -14,7 +14,8 @@ enum testCase
 	INSERTION_SORT,
 	SHELL_SORT,
 	MERGE_SORT,
-	QUICK_SORT
+	QUICK_SORT,
+	COUNTING_SORT
 };
 
 void linearSearchTest();
@@ -25,10 +26,11 @@ void insertionSortTest();
 void shellSortTest();
 void mergeSortTest();
 void quickSortTest();
+void countingSortTest();
 
 int main()
 {
-	testCase test = QUICK_SORT;
+	testCase test = COUNTING_SORT;
 
 	switch (test)
 	{
@@ -64,6 +66,10 @@ int main()
 		quickSortTest();
 		break;
 
+	case COUNTING_SORT:
+		countingSortTest();
+		break;
+
 	default:
 		break;
 	}
@@ -552,5 +558,41 @@ void quickSortTest()
 	std::cout << "\nAfter sorting in descending order, the lists contains: ";
 	quickDoubleSort.printArray();
 
+	std::cout << "\n";
+}
+
+void countingSortTest()
+{
+	std::cout << "Counting sort test\n\n";
+
+	//Initialize a empty vector to store value
+	std::vector<int>    intList;
+	std::vector<double> doubleList;
+
+	//initialize random seeds
+	srand((unsigned int)time(NULL));
+
+	//Push value to the list
+	std::cout << "list contains the followings elements: \n";
+	int randomValue;
+	for (int iter = 0; iter < 20; ++iter) {
+		randomValue = rand() % 250 + 1;
+		intList.push_back(randomValue);
+		std::cout << randomValue << " ";
+	}
+	std::cout << "\n";
+
+	//Sort the list in ascending order
+	sortAlgorithms::countingSort(intList, true);
+
+	std::cout << "\nAfter sorting in ascending order, the lists contains: ";
+	sortAlgorithms::printArray(intList);
+
+	//Sort the list in descending order
+	sortAlgorithms::countingSort(intList, false);
+
+	std::cout << "\nAfter sorting in descending order, the lists contains: ";
+	sortAlgorithms::printArray(intList);
+
 	std::cout << "\n";
 }
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