update merge-sort to reflect API update

sorting.cpp

-#include<iostream>
-#include<vector>
 #include "sorting.h"
+#include<iostream>
 
-using namespace std;
 
-vector<int> merge_fun(vector<int> array1, vector<int> array2){
-	int n1=array1.size(), n2=array2.size(),count1=0,count2=0;
-	vector<int> merged(n1+n2);
-	for(int i=0;i<n1+n2;i++){
-		if(count1>=n1){
-			merged[i]=array2[count2];
-			count2++;
-		}
-		else if(count2>=n2){
-			merged[i]=array1[count1];
-			count1++;
-		}
-		else{
-			if(array1[count1]<=array2[count2]){
-				merged[i]=array1[count1];
-				count1++;
-			}
-			else{
-				merged[i]=array2[count2];
-				count2++;
-			}
-		}
-	}
-	return merged;
+void merge(vector<int>& inp, int start, int middle, int end) {
+	int p = start,q = middle+1;
+	int array[end-start+1] ;
+	int k=0 ;
+	for(int i=start;i<=end;i++) {
+	    if(p>middle)
+	        array[k++] = inp[q++] ;
+	    else if(q>end)
+	        array[k++] = inp[p++];
+	    else if(inp[p]<inp[q])
+	        array[k++] = inp[p++];
+	    else
+	        array[k++] = inp[q++];
+    }
+    for(int i=start ; i<=end ; i++){
+    	inp[i]=array[i-start] ;
+    }
 }
-vector<int> sort_custom(vector<int> inp){
-	int n=inp.size();
-	if(n==1){
-		return inp;
-	}
-	else
-	{
-		int n1=n/2;
-		int n2=n-n1;
-		vector<int> array1(n1),array2(n2);
-		for(int i=0;i<n;i++){
-			if(i<n1)
-				array1[i]=inp[i];
-			else if(i<n1+n2)
-				array2[i - n1]=inp[i];
-		}
-		vector<int> out1=sort_custom(array1);
-		vector<int> out2=sort_custom(array2);
-		vector<int> ans=merge_fun(out1,out2);
-		return ans;
+
+
+void merge_sort(vector<int>& inp, int start, int end)
+{
+	if(start < end){
+		int middle = (start + end)/2 ;
+	    merge_sort(inp,start,middle) ;
+	    merge_sort(inp,middle+1,end) ;
+	    merge(inp,start,middle,end); 
 	}
+}
+
+
+vector<int> sort_custom(vector<int> inp, int startidx, int endidx){
+    merge_sort(inp,startidx,endidx) ; 
+	return inp;
 }
\ No newline at end of file