Replace every array element by Bitwise Xor of previous and next element

• Difficulty Level : Easy
• Last Updated : 07 Jul, 2021

Given an array of integers, replace every element with xor of previous and next elements with following exceptions.
a) First element is replaced by sum of first and second.
b) Last element is replaced by sum of last and second last.

Examples:

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

```Input: arr[] = { 2, 3, 4, 5, 6}
Output: 1 6 6 2 3

We get the following array as {2^3, 2^4, 3^5, 4^6, 5^6}

Input: arr[] = { 1, 2, 1, 5}
Output: 3, 0, 7, 4

We get the following array as {1^2, 1^1, 2^5, 1^5}
```

A Simple Solution is to create an auxiliary array, copy contents of given array to auxiliary array. Finally traverse the auxiliary array and update given array using copied values. Time complexity of this solution is O(n), but it requires O(n) extra space.

An efficient solution can solve the problem in O(n) time and O(1) space. The idea is to keep track of previous element in loop. Xor the previous element using the extra variable and the next element to get each element.

Below is the implementation of the above approach:

C++

 `// C++ program to update every array element with``// sum of previous and next numbers in array``#include ``using` `namespace` `std;` `void` `ReplaceElements(``int` `arr[], ``int` `n)``{``    ``// Nothing to do when array size is 1``    ``if` `(n <= 1)``        ``return``;` `    ``// store current value of arr[0] and update it``    ``int` `prev = arr[0];``    ``arr[0] = arr[0] ^ arr[1];` `    ``// Update rest of the array elements``    ``for` `(``int` `i = 1; i < n - 1; i++) {``        ``// Store current value of next interaction``        ``int` `curr = arr[i];` `        ``// Update current value using previous value``        ``arr[i] = prev ^ arr[i + 1];` `        ``// Update previous value``        ``prev = curr;``    ``}` `    ``// Update last array element separately``    ``arr[n - 1] = prev ^ arr[n - 1];``}` `// Driver program``int` `main()``{``    ``int` `arr[] = { 2, 3, 4, 5, 6 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);` `    ``ReplaceElements(arr, n);` `    ``// Print the modified array``    ``for` `(``int` `i = 0; i < n; i++)``        ``cout << arr[i] << ``" "``;``    ``return` `0;``}`

Java

 `// Java  program to update every array``// element with sum of previous and``// next numbers in array``import`  `java .io.*;` `class` `GFG``{``static` `void` `ReplaceElements(``int``[] arr,``                            ``int` `n)``{``    ``// Nothing to do when array size is 1``    ``if` `(n <= ``1``)``        ``return``;` `    ``// store current value of arr[0]``    ``// and update it``    ``int` `prev = arr[``0``];``    ``arr[``0``] = arr[``0``] ^ arr[``1``];` `    ``// Update rest of the array elements``    ``for` `(``int` `i = ``1``; i < n - ``1``; i++)``    ``{``        ``// Store current value of``        ``// next interaction``        ``int` `curr = arr[i];` `        ``// Update current value using``        ``// previous value``        ``arr[i] = prev ^ arr[i + ``1``];` `        ``// Update previous value``        ``prev = curr;``    ``}` `    ``// Update last array element separately``    ``arr[n - ``1``] = prev ^ arr[n - ``1``];``}` `// Driver Code``public` `static` `void` `main(String[] args)` `{``    ``int``[] arr = { ``2``, ``3``, ``4``, ``5``, ``6` `};``    ``int` `n = arr.length;` `    ``ReplaceElements(arr, n);` `    ``// Print the modified array``    ``for` `(``int` `i = ``0``; i < n; i++)``        ``System.out.print(arr[i] + ``" "``);``}``}` `// This code is contributed``// by anuj_67..`

Python3

 `# Python3 program to update every``# array element with sum of previous``# and next numbers in array``def` `ReplaceElements(arr, n):` `    ``# Nothing to do when array``    ``# size is 1``    ``if` `n <``=` `1``:``        ``return` `    ``# store current value of arr[0]``    ``# and update it``    ``prev ``=` `arr[``0``]``    ``arr[``0``] ``=` `arr[``0``] ^ arr[``1``]` `    ``# Update rest of the array elements``    ``for` `i ``in` `range``(``1``, n ``-` `1``):` `        ``# Store current value of``        ``# next interaction``        ``curr ``=` `arr[i]``        ` `        ``# Update current value using``        ``# previous value``        ``arr[i] ``=` `prev ^ arr[i ``+` `1``]``        ` `        ``# Update previous value``        ``prev ``=` `curr``    ` `    ``# Update last array element separately``    ``arr[n ``-` `1``] ``=` `prev ^ arr[n ``-` `1``]` `# Driver Code``arr ``=` `[``2``, ``3``, ``4``, ``5``, ``6``]``n ``=` `len``(arr)``ReplaceElements(arr, n)``for` `i ``in` `range``(n):``    ``print``(arr[i], end ``=` `" "``)` `# This code is contributed``# by Shrikant13`

C#

 `// C# program to update every array``// element with sum of previous and``// next numbers in array``using` `System;` `class` `GFG``{``static` `void` `ReplaceElements(``int``[] arr,``                            ``int` `n)``{``    ``// Nothing to do when array size is 1``    ``if` `(n <= 1)``        ``return``;` `    ``// store current value of arr[0]``    ``// and update it``    ``int` `prev = arr[0];``    ``arr[0] = arr[0] ^ arr[1];` `    ``// Update rest of the array elements``    ``for` `(``int` `i = 1; i < n - 1; i++)``    ``{``        ``// Store current value of``        ``// next interaction``        ``int` `curr = arr[i];` `        ``// Update current value using``        ``// previous value``        ``arr[i] = prev ^ arr[i + 1];` `        ``// Update previous value``        ``prev = curr;``    ``}` `    ``// Update last array element separately``    ``arr[n - 1] = prev ^ arr[n - 1];``}` `// Driver Code``public` `static` `void` `Main()``{``    ``int``[] arr = { 2, 3, 4, 5, 6 };``    ``int` `n = arr.Length;` `    ``ReplaceElements(arr, n);` `    ``// Print the modified array``    ``for` `(``int` `i = 0; i < n; i++)``        ``Console.Write(arr[i] + ``" "``);``}``}` `// This code is contributed``// by Akanskha Rai(Abby_akku)`

PHP

 ``

Javascript

 ``
Output:
`1 6 6 2 3`

My Personal Notes arrow_drop_up