# Number of co-prime pairs in an array

• Difficulty Level : Basic
• Last Updated : 28 Apr, 2021

Co-prime or mutually prime pair are those pair of numbers whose GCD is 1. Given an array of size n, find number of Co-Prime or mutually prime pairs in the array.

Examples:

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```Input : 1 2 3
Output : 3
Here, Co-prime pairs are ( 1, 2), ( 2, 3),
( 1, 3)

Input :4 8 3 9
Output :4
Here, Co-prime pairs are  ( 4, 3), ( 8, 3),
( 4, 9 ), ( 8, 9 )  ```

Approach : Using two loop, check every possible pair of the array. If Gcd of the pair is 1 increment counter value and at last display it.

## C++

 `// C++ program to find``// number of co-prime``// pairs in array``#include ``using` `namespace` `std;` `// function to check for gcd``bool` `coprime(``int` `a, ``int` `b)``{  ``    ``return` `(__gcd(a, b) == 1);``}` `// Recursive function to``// return gcd of a and b``int` `numOfPairs(``int` `arr[], ``int` `n)``{``    ` `    ``int` `count = 0;``    ``for` `(``int` `i = 0; i < n - 1; i++)``        ``for` `(``int` `j = i + 1; j < n; j++)``            ``if` `(coprime(arr[i], arr[j]))``                ``count++;``                ` `    ``return` `count;``}` `// driver code``int` `main()``{``    ``int` `arr[] = { 1, 2, 5, 4, 8, 3, 9 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``cout << numOfPairs(arr, n);``    ``return` `0;``}`

## Java

 `// Java program to find``// number of co-prime``// pairs in array``import` `java.io.*;` `class` `GFG {``    ` `    ``// Recursive function to``    ``// return gcd of a and b``    ``static` `int` `gcd(``int` `a, ``int` `b)``    ``{``        ``// Everything divides 0``        ``if` `(a == ``0` `|| b == ``0``)``        ``return` `0``;``    ` `        ``// base case``        ``if` `(a == b)``            ``return` `a;``    ` `        ``// a is greater``        ``if` `(a > b)``            ``return` `gcd(a-b, b);``            ` `        ``return` `gcd(a, b-a);``    ``}``    ` `    ``// function to check for gcd``    ``static` `boolean` `coprime(``int` `a, ``int` `b)``    ``{``        ``return` `(gcd(a, b) == ``1``);``    ``}``    ` `    ``// Returns count of co-prime``    ``// pairs present in array``    ``static` `int` `numOfPairs(``int` `arr[], ``int` `n)``    ``{``        ` `        ``int` `count = ``0``;``        ``for` `(``int` `i = ``0``; i < n - ``1``; i++)``            ``for` `(``int` `j = i + ``1``; j < n; j++)``                ``if` `(coprime(arr[i], arr[j]))``                    ``count++;``                    ` `        ``return` `count;``    ``}``    ` `    ``// driver code``    ``public` `static` `void` `main(String args[])``                            ``throws` `IOException``    ``{``        ``int` `arr[] = { ``1``, ``2``, ``5``, ``4``, ``8``, ``3``, ``9` `};``        ``int` `n = arr.length;``        ` `        ``System.out.println(numOfPairs(arr, n));``    ``}``}` `/* This code is contributed by Nikita Tiwari.*/`

## Python3

 `# Python 3 program to``# find number of co``# prime pairs in array` `# Recursive function to``# return gcd of a and b``def` `gcd(a, b):``    ` `    ``# Everything divides 0``    ``if` `(a ``=``=` `0` `or` `b ``=``=` `0``):``        ``return` `False``    ` `    ` `    ``# base case``    ``if` `(a ``=``=` `b):``        ``return` `a` `    ``# a is greater``    ``if` `(a > b):``        ``return` `gcd(a``-``b, b)``        ` `    ``return` `gcd(a, b``-``a)``    ` `# function to check``# for gcd``def` `coprime(a, b) :``    ``return` `(gcd(a, b) ``=``=` `1``)`  `# Returns count of``# co-prime pairs``# present in array``def` `numOfPairs(arr, n) :``    ``count ``=` `0``    ` `    ``for` `i ``in` `range``(``0``, n``-``1``) :``        ``for` `j ``in` `range``(i``+``1``, n) :``    ` `            ``if` `(coprime(arr[i], arr[j])) :``                ``count ``=` `count ``+` `1``    ` `    ``return` `count`  `# driver code``arr ``=` `[``1``, ``2``, ``5``, ``4``, ``8``, ``3``, ``9``]``n ``=` `len``(arr)` `print``(numOfPairs(arr, n))` `# This code is contributed by Nikita Tiwari.`

## C#

 `// C# program to find number of``// co-prime pairs in array``using` `System;` `class` `GFG {``    ` `    ``// Recursive function to``    ``// return gcd of a and b``    ``static` `int` `gcd(``int` `a, ``int` `b)``    ``{``        ``// Everything divides 0``        ``if` `(a == 0 || b == 0)``        ``return` `0;``    ` `        ``// base case``        ``if` `(a == b)``            ``return` `a;``    ` `        ``// a is greater``        ``if` `(a > b)``            ``return` `gcd(a-b, b);``            ` `        ``return` `gcd(a, b-a);``    ``}``    ` `    ``// function to check for gcd``    ``static` `bool` `coprime(``int` `a, ``int` `b)``    ``{``        ``return` `(gcd(a, b) == 1);``    ``}``    ` `    ``// Returns count of co-prime``    ``// pairs present in array``    ``static` `int` `numOfPairs(``int` `[]arr, ``int` `n)``    ``{``        ` `        ``int` `count = 0;``        ``for` `(``int` `i = 0; i < n - 1; i++)``            ``for` `(``int` `j = i + 1; j < n; j++)``                ``if` `(coprime(arr[i], arr[j]))``                    ``count++;``                    ` `        ``return` `count;``    ``}``    ` `    ``// driver code``    ``public` `static` `void` `Main()``    ``{``        ``int` `[]arr = { 1, 2, 5, 4, 8, 3, 9 };``        ``int` `n = arr.Length;``        ` `        ``Console.WriteLine(numOfPairs(arr, n));``    ``}``}` `//This code is contributed by Anant Agarwal.`

## PHP

 ` ``\$b``)``        ``return` `__gcd(``\$a` `- ``\$b``, ``\$b``);``    ``return` `__gcd(``\$a``, ``\$b` `- ``\$a``);``}` `// function to check for gcd``function` `coprime(``\$a``, ``\$b``)``{``    ``return` `(__gcd(``\$a``, ``\$b``) == 1);``}` `// Recursive function to``// return gcd of a and b``function` `numOfPairs(``\$arr``, ``\$n``)``{``    ` `    ``\$count` `= 0;``    ``for` `( ``\$i` `= 0; ``\$i` `< ``\$n` `- 1; ``\$i``++)``        ``for` `(``\$j` `= ``\$i` `+ 1; ``\$j` `< ``\$n``; ``\$j``++)``            ``if` `(coprime(``\$arr``[``\$i``], ``\$arr``[``\$j``]))``                ``\$count``++;``                ` `    ``return` `\$count``;``}``    ` `    ``// Driver code``    ``\$arr` `= ``array``(1, 2, 5, 4, 8, 3, 9);``    ``\$n` `= ``count``(``\$arr``);``    ``echo` `numOfPairs(``\$arr``, ``\$n``);``    ` `// This code is contributed by anuj_67.``?>`

## Javascript

 ``

Output:

`17`

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