Sorting algorithm added

Algorithms/counting_sort.cpp

@@ -0,0 +1,73 @@
+#include <iostream>
+#include <algorithm>
+#include <cmath>
+using namespace std;
+
+/*
+Counting sort implementation for sorting given array.
+Note - Works on Non-negative integer array only.
+
+Parameters:
+int a[] - Integer array a to be sorted.
+int n	- size of array a.
+int r.	- Range of numbers in a.
+*/
+
+void counting_sort(int a[], int n, int r) {
+	if(a == NULL) return;
+
+	int *cnt = new int[r+1]; //array to store count of each occurences
+	int *out = new int[n]; //Out array to store sorted values
+
+
+	// Intitialise the count array to 0
+	for (int i = 0; i <= r; ++i)
+		cnt[i] = 0;
+
+	// Count each occurences digit wise
+	for (int i = 0; i < n; ++i)
+		cnt[a[i]]++;
+
+	// Cumulative count array
+	for (int i = 1; i <= r; ++i)
+		cnt[i]+=cnt[i-1];
+
+	// Sort
+	for (int i = n - 1; i >= 0; i--) {
+		// Note - starting from n-1 to maintain "stable sort" property
+		out[cnt[a[i]] - 1] = a[i];
+		cnt[a[i]]--;
+	}
+
+	// Copy results back to orignal array
+	for (int i = 0; i < n; i++)
+		a[i] = out[i];
+}
+
+
+int main() {
+	ios_base::sync_with_stdio(false); //For faster io
+	int a[] = {1, 2, 9, 293, 41, 15, 52, 3, 121, 7, 1223, 3449, 15, 1 };
+	int n = sizeof(a)/sizeof(a[0]);
+
+	// Get the iterator to max element for calculating range of number
+	int * max_a_itr = max_element(a, a+n);
+	int max_a = *max_a_itr;
+
+
+	cout << "Input Array:\n";
+	for (int i = 0; i < n; i++) {
+		cout << a[i] << " ";
+	}
+	cout << "\n";
+
+	counting_sort(a, n, max_a);
+
+	cout << "Sorted Array:\n";
+	for (int i = 0; i < n; i++) {
+		cout << a[i] << " ";
+	}
+	cout << "\n";
+
+	return 0;
+}