change implementation to merge-sort

sorting.cpp

 #include "sorting.h"
 
-vector<int> sort_custom(vector<int> a)
+vector<int> merge(vector<int> left, vector<int> right)
 {
-   bool swapp = true;
-      while(swapp){
-        swapp = false;
-        for (size_t i = 0; i < a.size()-1; i++) {
-            if (a[i]>a[i+1] ){
-                a[i] += a[i+1];
-                a[i+1] = a[i] - a[i+1];
-                a[i] -=a[i+1];
-                swapp = true;
-            }
-        }
-    }
-  return a;
+   vector<int> result;
+   while ((int)left.size() > 0 || (int)right.size() > 0) {
+      if ((int)left.size() > 0 && (int)right.size() > 0) {
+         if ((int)left.front() <= (int)right.front()) {
+            result.push_back((int)left.front());
+            left.erase(left.begin());
+         } 
+   else {
+            result.push_back((int)right.front());
+            right.erase(right.begin());
+         }
+      }  else if ((int)left.size() > 0) {
+            for (int i = 0; i < (int)left.size(); i++)
+               result.push_back(left[i]);
+            break;
+      }  else if ((int)right.size() > 0) {
+            for (int i = 0; i < (int)right.size(); i++)
+               result.push_back(right[i]);
+            break;
+      }
+   }
+   return result;
 }
+
+vector<int> sort_custom(vector<int> m)
+{
+   if (m.size() <= 1)
+      return m;
+ 
+   vector<int> left, right, result;
+   int middle = ((int)m.size()+ 1) / 2;
+ 
+   for (int i = 0; i < middle; i++) {
+      left.push_back(m[i]);
+   }
+
+   for (int i = middle; i < (int)m.size(); i++) {
+      right.push_back(m[i]);
+   }
+ 
+   left = sort_custom(left);
+   right = sort_custom(right);
+   result = merge(left, right);
+ 
+   return result;
+}
+