update implementation to merge sort

sorting.cpp

@@ -32,13 +32,13 @@ vector<int> sort_custom(vector<int> m)
       return m;
  
    vector<int> left, right, result;
-   int middle = ((int)m.size()+ 1) / 2;
+   int mid = ((int)m.size()+ 1) / 2;
  
-   for (int i = 0; i < middle; i++) {
+   for (int i = 0; i < mid; i++) {
       left.push_back(m[i]);
    }
 
-   for (int i = middle; i < (int)m.size(); i++) {
+   for (int i = mid; i < (int)m.size(); i++) {
       right.push_back(m[i]);
    }