change implementation to merge-sort

sorting.cpp

 #include<iostream>
+#include<vector>
 #include "sorting.h"
 using namespace std;
+vector<int> merge(vector<int> arr1, vector<int> arr2){
+	int n1=arr1.size(), n2=arr2.size(),count1=0,count2=0;
+	vector<int> mergedArray(n1+n2);
+	for(int i=0;i<n1+n2;i++){
+		if(count1>=n1){
+			mergedArray[i]=arr2[count2];
+			count2++;
+		}
+		else if(count2>=n2){
+			mergedArray[i]=arr1[count1];
+			count1++;
+		}
+		else{
+			if(arr1[count1]<=arr2[count2]){
+				mergedArray[i]=arr1[count1];
+				count1++;
+			}
+			else{
+				mergedArray[i]=arr2[count2];
+				count2++;
+			}
+		}
+	}
+	return mergedArray;
+}
 vector<int> sort_custom(vector<int> arr){
-	int N=arr.size();
-	for(int i=0;i<N;i++)
-		for(int j=0;j<N-i-1;j++)
-			if(arr[j]>arr[j+1])
-				swap(arr[j],arr[j+1]);
-	return arr;
+	int n=arr.size();
+	if(n==1){
+		return arr;
+	}
+	else
+	{
+		int n1=n/2;
+		int n2=n-n1;
+		vector<int> arr1(n1),arr2(n2);
+		for(int i=0;i<n;i++){
+			if(i<n1)
+				arr1[i]=arr[i];
+			else if(i<n1+n2)
+				arr2[i - n1]=arr[i];
+		}
+		vector<int> ans1=sort_custom(arr1);
+		vector<int> ans2=sort_custom(arr2);
+		vector<int> ans=merge(ans1,ans2);
+		return ans;
+	}
 }