added MergeSort.cpp and updated README.md

Author: xshthkr

README.md

@@ -3150,8 +3150,8 @@ In order to achieve greater coverage and encourage more people to contribute to
                 </a>
             </td>
             <td> <!-- C++ -->
-                <a href="./CONTRIBUTING.md">
-                    <img align="center" height="25" src="./logos/github.svg" />
+                <a href="./src/cpp/MergeSort.cpp">
+                    <img align="center" height="25" src="./logos/cplusplus.svg" />
                 </a>
             </td>
             <td> <!-- Java -->

src/cpp/MergeSort.cpp

@@ -0,0 +1,107 @@
+#include <iostream>
+#include <vector>
+
+/**
+ * Merge two sub-arrays of arr[]
+ * - First sub-array is arr[left..mid]
+ * - Second sub-array is arr[mid+1..right]
+ *
+ * @param arr   The array to be sorted
+ * @param left  The left index of the first sub-array
+ * @param mid   The right index of the first sub-array
+ * @param right The right index of the second sub-array
+ */
+
+void merge(std::vector<int>& arr, int left, int mid, int right) {
+
+    int n1 = mid - left + 1;  // size of the first sub-array.
+    int n2 = right - mid;     // size of the second sub-array.
+
+    // create temporary arrays to hold the data
+    std::vector<int> leftSubarray(n1);
+    std::vector<int> rightSubarray(n2);
+
+    // copy data to temporary arrays leftSubarray[] and rightSubarray[]
+    for (int i = 0; i < n1; i++) {
+        leftSubarray[i] = arr[left + i];
+    }
+    for (int j = 0; j < n2; j++) {
+        rightSubarray[j] = arr[mid + 1 + j];
+    }
+
+    // merge the two sub-arrays back into the original array arr[]
+    int i = 0, j = 0, k = left;
+
+    while (i < n1 && j < n2) {
+        if (leftSubarray[i] <= rightSubarray[j]) {
+            arr[k] = leftSubarray[i];
+            i++;
+        }
+        else {
+            arr[k] = rightSubarray[j];
+            j++;
+        }
+        k++;
+    }
+
+    // copy the remaining elements of leftSubarray[], if any
+    while (i < n1) {
+        arr[k] = leftSubarray[i];
+        i++;
+        k++;
+    }
+
+    // copy the remaining elements of rightSubarray[], if any
+    while (j < n2) {
+        arr[k] = rightSubarray[j];
+        j++;
+        k++;
+    }
+}
+
+
+
+/**
+ * Merge Sort algorithm
+ *
+ * @param arr   The array to be sorted
+ * @param left  The left index of the sub-array to be sorted
+ * @param right The right index of the sub-array to be sorted
+ */
+
+void mergeSort(std::vector<int>& arr, int left, int right) {
+    if (left < right) {
+
+        int mid = left + (right - left) / 2;  // calculate the middle index
+
+        // sort the first and second halves
+        mergeSort(arr, left, mid);
+        mergeSort(arr, mid + 1, right);
+
+        // merge the sorted halves
+        merge(arr, left, mid, right);
+    }
+}
+
+int main() {
+
+    std::vector<int> arr = {12, 11, 13, 5, 6, 7, 9, 4, 10, 9, 11, 1, 11};
+
+    int arrSize = arr.size();
+
+    std::cout << "Original array: ";
+    for (int num : arr) {
+        std::cout << num << " ";
+    }
+    std::cout << std::endl;
+
+    mergeSort(arr, 0, arrSize - 1);
+
+    std::cout << "Sorted array: ";
+    for (int num : arr) {
+        std::cout << num << " ";
+    }
+    std::cout << std::endl;
+
+    return 0;
+}