Added Merge Sort implementation in C (Fixes #212)

Author: AyushAnand413

C/algorithms/sorting/merge_sort.c

@@ -0,0 +1,104 @@
+
+/*
+ * Algorithm: Merge Sort
+ * Description: A divide-and-conquer sorting algorithm that recursively splits the array, sorts the halves, and merges them in order.
+ * Time Complexity: O(n log n) for best, average, and worst cases
+ * Space Complexity: O(n) due to temporary arrays used during merging
+ * Author: Ayush Anand
+ * Date: 2025-10-01
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+// Function to merge two sorted subarrays
+void merge(int arr[], int left, int mid, int right) {
+    int n1 = mid - left + 1; // Size of left subarray
+    int n2 = right - mid;    // Size of right subarray
+
+    // Dynamically allocate temporary arrays
+    int *L = (int *)malloc(n1 * sizeof(int));
+    int *R = (int *)malloc(n2 * sizeof(int));
+
+    if (L == NULL || R == NULL) {
+        printf("Memory allocation failed!\n");
+        exit(1);
+    }
+
+    // Copy data to temporary arrays L[] and R[]
+    for (int i = 0; i < n1; i++)
+        L[i] = arr[left + i];
+    for (int j = 0; j < n2; j++)
+        R[j] = arr[mid + 1 + j];
+
+    // Merge the temporary arrays back into arr[left..right]
+    int i = 0, j = 0, k = left;
+
+    while (i < n1 && j < n2) {
+        if (L[i] <= R[j]) {
+            arr[k++] = L[i++];
+        } else {
+            arr[k++] = R[j++];
+        }
+    }
+
+    // Copy remaining elements, if any
+    while (i < n1)
+        arr[k++] = L[i++];
+    while (j < n2)
+        arr[k++] = R[j++];
+
+    // Free dynamically allocated memory
+    free(L);
+    free(R);
+}
+
+// Recursive function to implement Merge Sort
+void mergeSort(int arr[], int left, int right) {
+    if (left < right) {
+        int mid = left + (right - left) / 2;
+
+        // Recursively sort first and second halves
+        mergeSort(arr, left, mid);
+        mergeSort(arr, mid + 1, right);
+
+        // Merge the sorted halves
+        merge(arr, left, mid, right);
+    }
+}
+
+// Function to print an array
+void printArray(int arr[], int size) {
+    for (int i = 0; i < size; i++)
+        printf("%d ", arr[i]);
+    printf("\n");
+}
+
+// Driver code
+int main() {
+    int n;
+
+    printf("Enter the number of elements: ");
+    scanf("%d", &n);
+
+    int *arr = (int *)malloc(n * sizeof(int));
+    if (arr == NULL) {
+        printf("Memory allocation failed!\n");
+        return 1;
+    }
+
+    printf("Enter %d elements:\n", n);
+    for (int i = 0; i < n; i++)
+        scanf("%d", &arr[i]);
+
+    printf("Original array: ");
+    printArray(arr, n);
+
+    mergeSort(arr, 0, n - 1);
+
+    printf("Sorted array:   ");
+    printArray(arr, n);
+
+    free(arr); // Free dynamically allocated memory
+    return 0;
+}