change implementation to insertion-sort

sorting.cpp

 #include "sorting.h"
 
-vector<int> sort_custom(vector<int> a)
-{
-   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> sort_custom(vector<int> arr){
+    int i, key, j;
+   for (i = 1; i < arr.size(); i++)
+   {
+       key = arr[i];
+       j = i-1;
+ 
+       /* Move elements of arr[0..i-1], that are
+          greater than key, to one position ahead
+          of their current position */
+       while (j >= 0 && arr[j] > key)
+       {
+           arr[j+1] = arr[j];
+           j = j-1;
+       }
+       arr[j+1] = key;
+   }
+ return arr;
 }
+