Maximum in an array that can make another array sorted in C++

We are given an array of numbers say Arr1[] and another array Arr2[] of same or different length. The Arr1[] has elements sorted in ascending order, such that a single element is unsorted. We must find the element from the second array Arr2[] such that it can replace the wrongly placed element of Arr1[] and make it sorted. Also, the element chosen from Arr2[] should be maximum if there are multiple options available.


Arr1[]= { 1,3,5,7,2,11 }, Arr2[]= { 4,8,7,10,9 }


Maximum element that can make Arr1 sorted: 10

Explanation − Numbers in Arr2[] that can make Arr1[] sorted − 8,9,10 as they all are >=7 and <=11. Out of these 10 is maximum.

New Arr1[] becomes { 1,3,5,7,10,11 } and is sorted.


Arr1[]= { 12,5,22,17 }, Arr2[]= { 4,8,7,10,9 }


No such element.

Explanation − No umbers in Arr2[] that are >=12 and <=22.

Arr1[] cannot be sorted.

Approach used in the below program is as follows

  • Arrays arr1[] and arr2[] are used to store numbers. Arr1[] is sorted in ascending order except one element.

  • Function sortMax( int arr1[], int arr2[], int n1, int n2 ) takes both arrays and their length and updates arr1[] if element in arr2[] is found that is maximum and can also replace incorrect element in arr[]

  • Store index of wrong placed element in arr1[] in variable wpos, initially -1.

  • maxx is used to store maximum among those elements of arr2[] that can replace wrongly placed element of arr1[] and make it sorted.

  • At first travers arr1[] and find incorrect element such. If arr[i]<arr[i-1]. Store index in wpos as i.

  • Now travers arr2[] and find elements that can be placed between arr1[wpos-1] and arr[wpos+1]. Also if such an element exists then compare it with maxx such element.

  • Update maximum.

  • In the end replace arr1[wpos] with maxx.

  • If such an element is found return maxx, else return -1.

  • If no element is found display a message.

  • Else print sorted arr1[].


 Live Demo

// C++ program to make array sorted
#include <bits/stdc++.h>
using namespace std;
int sortMax(int arr1[], int arr2[], int n1, int n2) //making arr1 sorted{
   int wpos=-1;
   int maxx=-1;
   int i,j;
      if(arr2[j]>=arr1[wpos-1] && arr2[j]<=arr1[wpos+1])
   return maxx;
int main(){
   int arr1[] = { 1, 3, 7, 4, 10 };
   int arr2[] = { 2, 1, 6, 8, 9 };
   int len1 = sizeof(arr1) / sizeof(arr1[0]);
   int len2 = sizeof(arr2) / sizeof(arr2[0]);
   int res=sortMax(arr1, arr2, len1, len2);
      cout<<"No swap possible! No such element!";
      cout<<"Maximum in arr2[] to make arr1[] sorted:"<<res;
      for(int i=0;i<len1;i++)
         cout<<arr1[i]<<" ";
      for(int i=0;i<len2;i++)
         cout<<arr2[i]<<" ";


Maximum in arr2[] to make arr1[] sorted:9
Arr1[]:1 3 7 9 10
Arr2[]:2 1 6 8 9

Updated on: 03-Aug-2020


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