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

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

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[0]);` `    ``// 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)), as we are using a loop for traversing n times and each time for checking if a number is prime or not we are using a loop to traverse sqrt(n) times which will cost O(sqrt(n)).

Auxiliary Space: O(1), as we are not using any extra space.

Previous
Next