From ced6ad67e1f5e79614fda699b7494e9d44322434 Mon Sep 17 00:00:00 2001
From: Paawan Mukker <paawan.mukker@ripl.ricoh.com>
Date: Wed, 10 Oct 2018 00:13:01 +0530
Subject: [PATCH] counting_sort.c: Add Counting Sort Algorithm

This adds Counting sort which sorts array by counting the occurences of elements.

Closes https://github.com/NITSkmOS/Algorithms/issues/381
---
 counting_sort/C/counting_sort.c | 73 +++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 counting_sort/C/counting_sort.c

diff --git a/counting_sort/C/counting_sort.c b/counting_sort/C/counting_sort.c
new file mode 100644
index 00000000..9e612b77
--- /dev/null
+++ b/counting_sort/C/counting_sort.c
@@ -0,0 +1,73 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+/*
+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;
+
+	 //array to store count of each occurences
+	int *cnt = (int *) malloc((r+1)*sizeof(int));  // Ignore CPPLintBear
+	//Out array to store sorted values
+	int *out = (int *) malloc((n)*sizeof(int));  // Ignore CPPLintBear
+
+
+	// 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() {
+	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 max element for calculating range of number
+	int max_a = a[0];
+	for (int i = 1; i < n; ++i)
+		if(max_a < a[i]) max_a = a[i];
+
+
+	printf("Input Array:\n");
+	for (int i = 0; i < n; i++) {
+		printf("%d ", a[i]);
+	}
+	printf("\n");
+
+	counting_sort(a, n, max_a);
+
+	printf("Sorted Array:\n");
+	for (int i = 0; i < n; i++) {
+		printf("%d ", a[i]);
+	}
+	printf("\n");
+
+	return 0;
+}