# XOR of all Prime numbers in an Array

• Difficulty Level : Basic
• Last Updated : 11 May, 2021

Given an array of integers arr[]. The task is to find the bitwise XOR of all the prime numbers present in the array.
Examples

```Input: arr[] = {2, 5, 8, 4, 3}
Output: 4

Input: arr[] = {7, 12, 2, 6, 11}
Output: 14```

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Approach:

• Create a sieve to check whether an element is prime or not in O(1).
• Traverse the array and check if the number is prime.
• Compute the xor of all the prime elements of the array.

Below is the implementation of the above approach:

## C++

 `// C++ program to find Xor of all``// Prime numbers in array` `#include ``using` `namespace` `std;` `bool` `prime[100005];` `void` `SieveOfEratosthenes(``int` `n)``{` `    ``memset``(prime, ``true``, ``sizeof``(prime));` `    ``// false here indicates``    ``// that it is not prime``    ``prime[1] = ``false``;` `    ``for` `(``int` `p = 2; p * p <= n; p++) {` `        ``// If prime[p] is not changed,``        ``// then it is a prime``        ``if` `(prime[p]) {` `            ``// Update all multiples of p,``            ``// set them to non-prime``            ``for` `(``int` `i = p * 2; i <= n; i += p)``                ``prime[i] = ``false``;``        ``}``    ``}``}` `// Function to compute xor of all``// prime elements``int` `xorPrimes(``int` `arr[], ``int` `n)``{``    ``SieveOfEratosthenes(100005);` `    ``int` `xorVal = 0;` `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``// if the element is prime``        ``if` `(prime[arr[i]])``            ``xorVal = xorVal ^ arr[i];``    ``}` `    ``return` `xorVal;``}` `// Driver code``int` `main()``{` `    ``int` `arr[] = { 4, 3, 2, 6, 100, 17 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);` `    ``cout << xorPrimes(arr, n);` `    ``return` `0;``}`

## Java

 `// Java program to find Xor of all``// Prime numbers in array``import` `java.util.Arrays;`  `class` `GFG``{``    ``static` `boolean` `prime[] = ``new` `boolean``[``100005``];` `    ``static` `void` `SieveOfEratosthenes(``int` `n)``    ``{``        ``Arrays.fill(prime, ``true``);` `        ``// false here indicates``        ``// that it is not prime``        ``prime[``1``] = ``false``;` `        ``for` `(``int` `p = ``2``; p * p < n; p++)``        ``{` `            ``// If prime[p] is not changed,``            ``// then it is a prime``            ``if` `(prime[p])``            ``{``                ``// Update all multiples of p,``                ``// set them to non-prime``                ``for` `(``int` `i = p * ``2``; i < n; i += p)``                ``{``                    ``prime[i] = ``false``;``                ``}``            ``}``        ``}``    ``}` `    ``// Function to compute xor of all``    ``// prime elements``    ``static` `int` `xorPrimes(``int` `arr[], ``int` `n)``    ``{``        ``SieveOfEratosthenes(``100005``);``        ``int` `xorVal = ``0``;``        ``for` `(``int` `i = ``0``; i < n; i++)``        ``{``            ``// if the element is prime``            ``if` `(prime[arr[i]])``            ``{``                ``xorVal = xorVal ^ arr[i];``            ``}``        ``}``        ``return` `xorVal;``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `arr[] = {``4``, ``3``, ``2``, ``6``, ``100``, ``17``};``        ``int` `n = arr.length;``        ``System.out.println(xorPrimes(arr, n));``    ``}``}` `// This code is contributed by``// Rajput-Ji`

## Python3

 `# Python3 program to find Xor of``# all Prime numbers in array` `prime ``=` `[``True``] ``*` `(``100005``)` `def` `SieveOfEratosthenes(n):`` ` `    ``# False here indicates``    ``# that it is not prime``    ``prime[``1``] ``=` `False``    ``p ``=` `2``    ` `    ``while` `p``*``p <``=` `n:` `        ``# If prime[p] is not changed,``        ``# then it is a prime``        ``if` `prime[p]: ` `            ``# Update all multiples of p,``            ``# set them to non-prime``            ``for` `i ``in` `range``(p ``*` `2``, n``+``1``, p):``                ``prime[i] ``=` `False``                ` `        ``p ``+``=` `1``         ` `# Function to compute xor``# of all prime elements``def` `xorPrimes(arr, n):`` ` `    ``SieveOfEratosthenes(``100004``)` `    ``xorVal ``=` `0``    ``for` `i ``in` `range``(``0``, n): ` `        ``# if the element is prime``        ``if` `prime[arr[i]]:``            ``xorVal ``=` `xorVal ^ arr[i]``     ` `    ``return` `xorVal`` ` `# Driver code``if` `__name__ ``=``=` `"__main__"``:`` ` `    ``arr ``=` `[``4``, ``3``, ``2``, ``6``, ``100``, ``17``] ``    ``n ``=` `len``(arr)` `    ``print``(xorPrimes(arr, n))` `# This code is contributed by Rituraj Jain`

## C#

 `// C# program to find Xor of all``// Prime numbers in array``using` `System;` `class` `GFG``{``    ``static` `bool` `[]prime = ``new` `bool``[100005];` `    ``static` `void` `SieveOfEratosthenes(``int` `n)``    ``{``        ``for``(``int` `i = 0; i < 100005; i++)``            ``prime[i] = ``true``;` `        ``// false here indicates``        ``// that it is not prime``        ``prime[1] = ``false``;` `        ``for` `(``int` `p = 2; p * p < n; p++)``        ``{` `            ``// If prime[p] is not changed,``            ``// then it is a prime``            ``if` `(prime[p])``            ``{``                ``// Update all multiples of p,``                ``// set them to non-prime``                ``for` `(``int` `i = p * 2; i < n; i += p)``                ``{``                    ``prime[i] = ``false``;``                ``}``            ``}``        ``}``    ``}` `    ``// Function to compute xor of all``    ``// prime elements``    ``static` `int` `xorPrimes(``int` `[]arr, ``int` `n)``    ``{``        ``SieveOfEratosthenes(100005);``        ``int` `xorVal = 0;``        ``for` `(``int` `i = 0; i < n; i++)``        ``{``            ``// if the element is prime``            ``if` `(prime[arr[i]])``            ``{``                ``xorVal = xorVal ^ arr[i];``            ``}``        ``}``        ``return` `xorVal;``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``        ``int` `[]arr = {4, 3, 2, 6, 100, 17};``        ``int` `n = arr.Length;``        ``Console.WriteLine(xorPrimes(arr, n));``    ``}``}` `/* This code contributed by PrinciRaj1992 */`

## Javascript

 ``
Output:
`16`

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