change implementation to merge-sort

sorting.cpp

-#include<iostream>
+
+#include<iostream> 
 #include "sorting.h"
+#include<vector>
 using namespace std;
+void merge(vector<int> &arr, int l, int m, int r) 
+{ 
+    int i, j, k; 
+    int n1 = m - l + 1; 
+    int n2 =  r - m; 
+    int L[n1], R[n2];
+    for (i = 0; i < n1; i++) 
+        L[i] = arr[l + i]; 
+    for (j = 0; j < n2; j++) 
+        R[j] = arr[m + 1+ j]; 
+    i = 0;  
+    j = 0; 
+    k = l; 
+    while (i < n1 && j < n2) 
+    { 
+        if (L[i] <= R[j]) 
+        { 
+            arr[k] = L[i]; 
+            i++; 
+        } 
+        else
+        { 
+            arr[k] = R[j]; 
+            j++; 
+        } 
+        k++; 
+    } 
+  
+    while (i < n1) 
+    { 
+        arr[k] = L[i]; 
+        i++; 
+        k++; 
+    } 
+  
+    while (j < n2) 
+    { 
+        arr[k] = R[j]; 
+        j++; 
+        k++; 
+    } 
+} 
+  
+
+void mergeSort(vector<int> &arr, int l, int r) 
+{ 
+    if (l < r) 
+    { 
+        
+        int m = l+(r-l)/2; 
+  
+        
+        mergeSort(arr, l, m); 
+        mergeSort(arr, m+1, r); 
+  
+        merge(arr, l, m, r); 
+    } 
+} 
 
-vector<int> sort_custom(vector<int> v1){
-   int i, j;
-   int n=v1.size();
-   for (i = 0; i < n-1; i++) {   
-       for (j = 0; j < n-i-1; j++){ 
-           if (v1[j] > v1[j+1])
-              swap(v1[j], v1[j+1]);
-        }
-    }
-    return v1;    
+vector<int> sort_custom(vector<int> data){
+	mergeSort(data,0,data.size()-1);
+	return data;
 }
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