Aman Saini's Blog

Rearrange an array such that ‘arr[j]’ becomes ‘i’ if ‘arr[i]’ is ‘j’ using C++

Aman Saini's photo
Aman Saini
·

3 min read

Hello learners, today in this tutorial we will learn how to rearrange an array such that ‘arr[j]’ becomes ‘i’ if ‘arr[i]’ is ‘j’ in C++ using an easy and comprehensible example. Let’s start with an example it will be more clear.

Let’s say we have an array of size N which contains distinct elements between 0 to ( N – 1). Our job is to rearrange the array elements so that array[i] = j is changed to arr[j] = i. Here is an example

Input: arr[ i ] = { 4, 1, 0, 2, 3, 6, 5 }. // ‘ i ‘ will iterate from 0 – (n-1).
Output: arr[] = { 2, 1, 3, 4, 0, 6, 5 }
Explanation:

arr[0] = 4 arr[4] = 0
arr[1] = 1 arr[1] = 1
arr[2] = 0 After rearranging arr[0] = 2
arr[3] = 2 =>=>=>=>=>=> arr[2] = 3
arr[4] = 3 arr[3] = 4
arr[5] = 6 arr[6] = 5
arr[6] = 5 arr[5] = 6

Firstly store all the elements of arr[] in another array using the code ” j [ arr [ i ] ] = i ”. Now print all the elements of the array.

Here is the code:

#include<bits/stdc++.h>
#include<string>
#include<algorithm>

using namespace std;

        void rearrange(int arr[], int n )
        {
            int j[n];

            // store value of j

            for (int i = 0; i < n; i++) 
            {
                j[arr[i]] = i;
            }

            for(int i=0;i<n;i++)
            {
                arr[i] = j[i];
            }

            std::cout <<"\n"<< "After Rearrangement : { ";
            for (int i = 0; i < n; i++) {
                std::cout << arr[i] << ", ";
            }
              cout<<"}";
        }

        int main()
        {

           int arr[] = { 4, 1, 0, 2, 3, 6, 5 }; 
           // number of elements in arr[].
            int n = sizeof(arr) / sizeof(arr[0]); 

            std::cout << "Initially Array : { ";
            for (int i = 0; i < n; i++) {
                std::cout << arr[i] <<", ";
            }
            cout<<"}";
            rearrange( arr, n);

            return 0;     
        }

Output:
Initially Array : { 4, 1, 0, 2, 3, 6, 5, }
After Rearrangement : { 2, 1, 3, 4, 0, 6, 5, }

Hope this article was helpful to you. Keep Coding Keep Learning.

C++