chore(CPlusPlus): created merge-sort (#324)

* Created merge-sort.cpp

* Updated README.md

* Added Example and Fixed Bug

algorithms/CPlusPlus/README.md

@@ -50,6 +50,7 @@
 10. [Radix Sort](Sorting/radix-sort.cpp)
 11. [Shell Sort](Sorting/shell-sort.cpp)
 12. [Binary Insertion Sort](Sorting/binary-insertion-sort.cpp)
+13. [Merge Sort](Sorting/merge-sort.cpp)
  
 ## Strings
 1. [Rabin-Karp pattern search algo](Strings/rabin-karp.cpp)

algorithms/CPlusPlus/Sorting/merge-sort.cpp

@@ -0,0 +1,66 @@
+//Description : Merge Sort Algorithm
+#include<bits/stdc++.h>
+using namespace std;
+
+void merging(int arr[], int l, int h, int m) {
+    int N1 = m - l + 1;                 //Left Array Size     
+    int N2 = h - m;                     //Right Array Size
+    int left[N1];                         
+    int right[N2];
+    for (int i = 0; i < N1; i++) {
+        left[i] = arr[l + i];          //Copy elements to left array
+    }
+    for (int j = 0; j < N2; j++) {
+        right[j] = arr[m + 1 + j];    //Copy elements to right array
+    }
+    int i = 0;
+    int j = 0;
+    int k = l;
+    while (i < N1 && j < N2) {       //Inserting back the elements from left and right array
+        if (left[i] <= right[j]) {   //If left element is smaller than the right one then we push 
+            arr[k++] = left[i++];    //left element to our main array(arr)   
+        } else {
+            arr[k++] = right[j++];   //else we push right element to the main array
+        }
+    }
+    for (; i < N1; i++) {            //These loop executes only when there is difference in size of
+        arr[k++] = left[i];          //left and right array
+    }
+    for (; j < N2; j++) {
+        arr[k++] = right[j];
+    }
+    return;
+}
+
+void merge_sort(int arr[], int l, int h) {
+    if (l < h) {
+        int mid = (l + ((h - l) / 2));
+        merge_sort(arr, l, mid);           //Recursively calling for elements before mid(including mid)
+        merge_sort(arr, mid + 1, h);       //Recursively calling for elements after mid
+        merging(arr, l, h, mid);           //Merging the two arrays
+    }
+    return;
+}
+int main() {
+    int arr[] = { 1,0,13,7,6,2,16 };
+    cout << "Array Before Sorting" << endl;
+    for (int i = 0; i < 7; i++) {
+        cout << arr[i] << " ";
+    }
+    cout << endl;
+    merge_sort(arr, 0, 6);
+    cout << "Array After Sorting" << endl;
+    for (int i = 0; i < 7; i++) {
+        cout << arr[i] << " ";
+    }
+    return 0;
+   //Ex :Input : arr= { 1,0,13,7,6,2,16 };
+   //    Output  
+   //    Array Before Sorting 
+   //    1 0 13 7 6 2 16
+   //    Array After Sorting
+   //    0 1 2 6 7 13 16
+   //Time Complexity :O(nlogn)
+   //Auxiliary Space :O(n)
+   //where n is the array size
+}