From 83ecf56d942842cf4a3ae66928e93ee8662d58a0 Mon Sep 17 00:00:00 2001
From: Shraddha <42699578+shraddhavp@users.noreply.github.com>
Date: Sun, 24 Oct 2021 12:36:59 +0530
Subject: [PATCH] Add merge sort with O(1) space (#2672)

---
 Sorts/MergeSortNoExtraSpace.java | 75 ++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 Sorts/MergeSortNoExtraSpace.java

diff --git a/Sorts/MergeSortNoExtraSpace.java b/Sorts/MergeSortNoExtraSpace.java
new file mode 100644
index 000000000..282082ece
--- /dev/null
+++ b/Sorts/MergeSortNoExtraSpace.java
@@ -0,0 +1,75 @@
+package Sorts;
+import java.util.Arrays;
+import java.util.*;
+
+/*This code implements the mergeSort algorithm without extra space
+For understanding about mergesort visit :https://www.geeksforgeeks.org/merge-sort/
+ */
+public class MergeSortNoExtraSpace {
+        public static void call_merge_sort(int a[],int n)
+        {
+            int maxele = Arrays.stream(a).max().getAsInt() + 1;
+            merge_sort(a,0,n-1,maxele);
+        }
+        public static void merge_sort(int a[],int start , int end,int maxele){ //this function divides the array into 2 halves
+
+            if(start<end){
+                int mid = (start +end)/2;
+                merge_sort(a, start,mid,maxele);
+                merge_sort(a,mid+1,end,maxele);
+                implement_merge_sort(a,start,mid,end,maxele);
+
+            }
+        }
+        public static void implement_merge_sort(int a[], int start , int mid , int end,int maxele){  //implementation of mergesort
+            int i=start;
+            int j=mid+1;
+            int k =start;
+            while (i<=mid && j<=end){
+                if(a[i]%maxele<=a[j]%maxele){
+                    a[k] = a[k] + (a[i]
+                            % maxele) * maxele;
+                    k++;
+                    i++;
+                }
+                else{
+                    a[k] = a[k] + (a[j]
+                            % maxele) * maxele;
+                    k++;
+                    j++;
+                }
+            }
+            while(i<=mid){
+                a[k] = a[k] + (a[i]
+                        % maxele) * maxele;
+                k++;
+                i++;
+            }
+            while(j<=end){
+                a[k] = a[k] + (a[j]
+                        % maxele) * maxele;
+                k++;
+                j++;
+            }
+            for(i=start;i<=end;i++)
+            {
+                a[i] = a[i] / maxele;
+            }
+
+        }
+        public static void main(String args[]) {
+            Scanner inp=new Scanner(System.in);
+            System.out.println("Enter array size");
+            int n=inp.nextInt();
+            int a[]=new int[n];
+            System.out.println("Enter array elements");
+            for(int i=0;i<n;i++)
+            {
+                a[i]=inp.nextInt();
+            }
+            call_merge_sort(a,n);
+            for(int i=0;i<a.length;i++){
+                System.out.print(a[i]+" ");
+            }
+        }
+    }