merge_sort.c: Add Merge Sort in C

This adds Merge Sort algorithm written in C

Closes NITSkmOS#147

README.md

@@ -14,7 +14,7 @@ This repository contains examples of various algorithms written on different pro
 |:----------------------------------------------------------------------------------------------- |:-------------------------------------:|:-------------------------------------:|:-------------------------------------:|:-------------------------------------:|
 | [Euclidean GCD](https://en.wikipedia.org/wiki/Euclidean_algorithm)                              | [:octocat:](euclidean_gcd/C)          |                                      | [:octocat:](euclidean_gcd/Java)        | [:octocat:](euclidean_gcd/Python)     |
 | [QuickSort](https://en.wikipedia.org/wiki/Quicksort)                                            |                                       |                                       |                                       | [:octocat:](quicksort/Python)         |
-| [Merge Sort](https://en.wikipedia.org/wiki/Merge_sort)                                          |                                       |                                       |                                       | [:octocat:](merge_sort/Python)        |
+| [Merge Sort](https://en.wikipedia.org/wiki/Merge_sort)                                          | [:octocat:](merge_sort/C)             |                                       |                                       | [:octocat:](merge_sort/Python)        |
 | [Insertion Sort](https://en.wikipedia.org/wiki/Insertion_sort)                                  | [:octocat:](insertion_sort/C)         | [:octocat:](insertion_sort/Cpp)       |                                       | [:octocat:](insertion_sort/Python)    |
 | [Counting Sort](https://en.wikipedia.org/wiki/Counting_sort)                                    |                                       | [:octocat:](counting_sort/Cpp)                                       |                                       | [:octocat:](counting_sort/Python)     |
 | [Radix Sort](https://en.wikipedia.org/wiki/Radix_sort)                                          |                                       | [:octocat:](radix_sort/Cpp)                                       |                                       | [:octocat:](radix_sort/Python)        |

merge_sort/C/merge_sort.c

@@ -0,0 +1,73 @@
+#include <stdio.h>	// for printf function
+
+// Function prototypes
+void mergesort(int[], int, int);
+void merge(int[], int, int, int);
+
+int main() {
+	int arr_size = 6;
+	int arr[6] = {10, 9, 8, 7, 6, 5};
+	mergesort(arr, 0, arr_size);
+
+	// Print sorted array
+	for (int i = 0; i < arr_size; i++) {
+		printf("%d ", arr[i]);
+	}
+	printf("\n");
+
+	return 0;
+}
+
+/*
+ * Recursively split the array and call the merge function
+ * Main entry point of Merge Sort
+ */
+void mergesort(int arr[], int l, int r) {
+	if(l >= r)
+		return;
+	int m = (l + r) / 2;
+	mergesort(arr, l, m);
+	mergesort(arr, m+1, r);
+	merge(arr, l, m, r);
+}
+
+// Merges the arrays in ascending order of elements
+void merge(int arr[], int l, int m, int r) {
+	int i, j, k;
+	int n1 = m - l + 1;
+	int n2 = r - m;
+
+	int L[n1], M[n2];
+
+	for(i = 0; i < n1; ++i)
+		L[i] = arr[l+i];
+	for(j = 0; j < n2; ++j)
+		M[j] = arr[m + 1 + j];
+
+	i = 0;
+	j = 0;
+	k = l;
+
+	while(i < n1 && j < n2) {
+		if(L[i] <= M[j]) {
+			arr[k] = L[i];
+			++i;
+		} else {
+			arr[k] = M[j];
+			++j;
+		}
+		++k;
+	}
+
+	while(i < n1) {
+		arr[k] = L[i];
+		++i;
+		++k;
+	}
+
+	while(j < n2) {
+		arr[k] = M[j];
+		++j;
+		++k;
+	}
+}