changed implementation to merge sort

sorting.cpp

@@ -2,22 +2,63 @@
 
 using namespace std;
 
-vector<int> sort_custom(vector<int> a)
+vector<int> merge(const vector<int>& left, const vector<int>& right)  
 {  
-    bool swapp = true;
-    while(swapp)
+    // Fill the resultant vector with sorted results from both vectors  
+    vector<int> result;  
+    unsigned left_it = 0, right_it = 0;  
+  
+    while(left_it < left.size() && right_it < right.size())  
     {  
-        swapp = false;
-        for (int i = 0; i < a.size()-1; i++)
+        // If the left value is smaller than the right it goes next  
+        // into the resultant vector  
+        if(left[left_it] < right[right_it])  
         {  
-            if (a[i]>a[i+1] )
+            result.push_back(left[left_it]);  
+            left_it++;  
+        }  
+        else  
         {  
-                a[i] += a[i+1];
-                a[i+1] = a[i] - a[i+1];
-                a[i] -=a[i+1];
-                swapp = true;
+            result.push_back(right[right_it]);  
+            right_it++;  
+        }  
     }  
+  
+    // Push the remaining data from both vectors onto the resultant  
+    while(left_it < left.size())  
+    {  
+        result.push_back(left[left_it]);  
+        left_it++;  
     }  
+  
+    while(right_it < right.size())  
+    {  
+        result.push_back(right[right_it]);  
+        right_it++;  
+    }  
+  
+    return result;  
+}  
+
+vector<int> sort_custom(vector<int> vec)  
+{  
+    // Termination condition: List is completely sorted if it  
+    // only contains a single element.  
+    if(vec.size() == 1)  
+    {  
+        return vec;  
     }  
-    return a;
+  
+    // Determine the location of the middle element in the vector  
+    std::vector<int>::iterator middle = vec.begin() + (vec.size() / 2);  
+  
+    vector<int> left(vec.begin(), middle);  
+    vector<int> right(middle, vec.end());  
+  
+    // Perform a merge sort on the two smaller vectors  
+    left = sort_custom(left);  
+    right = sort_custom(right);  
+  
+    return merge(left, right);  
 }  
+