# Find prime numbers in the first half and second half of an array

• Last Updated : 07 Apr, 2021

Given an array arr of size N. The task is to find the prime numbers in the first half (up to index N/2) and the second half (all the remaining elements) of an array.
Examples:

Input : arr[] = {2, 5, 10, 15, 17, 21, 23 }
Output :2 5 and 17 23
Prime numbers in the first half of an array are 2, 5 and in the second half are 17, 23
Input : arr[] = {31, 35, 40, 43}
Output :31 and 43

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Approach:
First Traverse the array up to N/2 and check all the elements whether they are prime or not and print the prime numbers. Then Traverse the array from N/2th element till N and find whether elements are prime or not and print all those elements which are prime.
Below is the implementation of the above approach:

## C++

 `// C++ program to print the prime numbers in the``// first half and second half of an array``#include ``using` `namespace` `std;` `// Function to check if a number is prime or not``bool` `prime(``int` `n)``{``    ``for` `(``int` `i = 2; i * i <= n; i++)``        ``if` `(n % i == 0)``            ``return` `false``;` `    ``return` `true``;``}` `// Function to find whether elements are prime or not``void` `prime_range(``int` `start, ``int` `end, ``int``* a)``{``    ``// Traverse in the given range``    ``for` `(``int` `i = start; i < end; i++) {` `        ``// Check if a number is prime or not``        ``if` `(prime(a[i]))``            ``cout << a[i] << ``" "``;``    ``}``}` `// Function to print the prime numbers in the``// first half and second half of an array``void` `Print(``int` `arr[], ``int` `n)``{` `    ``cout << ``"Prime numbers in the first half are "``;``    ``prime_range(0, n / 2, arr);``    ``cout << endl;` `    ``cout << ``"Prime numbers in the second half are "``;``    ``prime_range(n / 2, n, arr);``    ``cout << endl;``}` `// Driver Code``int` `main()``{` `    ``int` `arr[] = { 2, 5, 10, 15, 17, 21, 23 };` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);` `    ``// Function call``    ``Print(arr, n);` `    ``return` `0;``}`

## Java

 `// Java program to print the prime numbers in the``// first half and second half of an array``import` `java.util.*;` `class` `GFG``{` `// Function to check if``// a number is prime or not``static` `boolean` `prime(``int` `n)``{``    ``for``(``int` `i = ``2``; i * i <= n; i++)``        ``if``(n % i == ``0``)``            ``return` `false``;``            ` `    ``return` `true``;``}` `// Function to find whether elements``// are prime or not``static` `void` `prime_range(``int` `start,``                        ``int` `end, ``int``[] a)``{``    ``// Traverse in the given range``    ``for` `(``int` `i = start; i < end; i++)``    ``{``    ` `        ``// Check if a number is prime or not``        ``if``(prime(a[i]))``            ``System.out.print(a[i] + ``" "``);``    ``}``}`  `// Function to print the prime numbers in the``// first half and second half of an array``static` `void` `Print(``int` `arr[], ``int` `n)``{` `    ``System.out.print(``"Prime numbers in the first half are "``);``    ``prime_range(``0``, n / ``2``, arr);``    ``System.out.println();` `    ``System.out.print(``"Prime numbers in the second half are "``);``    ``prime_range(n / ``2``, n, arr);``    ``System.out.println();``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``    ``int` `arr[] = { ``2``, ``5``, ``10``, ``15``, ``17``, ``21``, ``23` `};` `    ``int` `n = arr.length;``    ` `    ``// Function call``    ``Print(arr, n);``}``}` `// This code is contributed by Princi Singh`

## Python3

 `# Python3 program to print the``# prime numbers in the first half``# and second half of an array` `# Function to check if``# a number is prime or not``def` `prime(n):` `    ``for` `i ``in` `range``(``2``, n):``        ``if` `i ``*` `i > n:``            ``break``        ``if``(n ``%` `i ``=``=` `0``):``            ``return` `False``;` `    ``return` `True``    ` `# Function to find whether``# elements are prime or not``def` `prime_range(start, end, a):``    ` `    ``# Traverse in the given range``    ``for` `i ``in` `range``(start, end):` `        ``# Check if a number is prime or not``        ``if``(prime(a[i])):``            ``print``(a[i], end ``=` `" "``)` `# Function to print the``# prime numbers in the first half``# and second half of an array``def` `Print``(arr, n):` `    ``print``(``"Prime numbers in the"``,``          ``"first half are "``, end ``=` `"")``    ``prime_range(``0``, n ``/``/` `2``, arr)``    ``print``()` `    ``print``(``"Prime numbers in the"``,``          ``"second half are "``, end ``=` `"")``    ``prime_range(n ``/``/` `2``, n, arr)``    ``print``()` `# Driver Code``arr ``=` `[``2``, ``5``, ``10``, ``15``, ``17``, ``21``, ``23``]` `n ``=` `len``(arr)` `# Function call``Print``(arr, n)` `# This code is contributed``# by Mohit Kumar`

## C#

 `// C# program to print the prime numbers in the``// first half and second half of an array``using` `System;``    ` `class` `GFG``{` `// Function to check if``// a number is prime or not``static` `Boolean prime(``int` `n)``{``    ``for``(``int` `i = 2; i * i <= n; i++)``        ``if``(n % i == 0)``            ``return` `false``;``            ` `    ``return` `true``;``}` `// Function to find whether elements``// are prime or not``static` `void` `prime_range(``int` `start,``                        ``int` `end, ``int``[] a)``{``    ``// Traverse in the given range``    ``for` `(``int` `i = start; i < end; i++)``    ``{``    ` `        ``// Check if a number is prime or not``        ``if``(prime(a[i]))``            ``Console.Write(a[i] + ``" "``);``    ``}``}`  `// Function to print the prime numbers in the``// first half and second half of an array``static` `void` `Print(``int` `[]arr, ``int` `n)``{` `    ``Console.Write(``"Prime numbers in the first half are "``);``    ``prime_range(0, n / 2, arr);``    ``Console.WriteLine();` `    ``Console.Write(``"Prime numbers in the second half are "``);``    ``prime_range(n / 2, n, arr);``    ``Console.WriteLine();``}` `// Driver Code``public` `static` `void` `Main(String[] args)``{``    ``int` `[]arr = { 2, 5, 10, 15, 17, 21, 23 };` `    ``int` `n = arr.Length;``    ` `    ``// Function call``    ``Print(arr, n);``}``}` `// This code is contributed by 29AjayKumar`

## Javascript

 ``
Output:
```Prime numbers in the first half are 2 5
Prime numbers in the second half are 17 23```

Time Complexity: O(n *  sqrt(n))

Auxiliary Space: O(1)

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