# Pairs from an array that satisfy the given condition

• Difficulty Level : Basic
• Last Updated : 14 Apr, 2021

Given an array arr[], the task is to count all the valid pairs from the array. A pair (arr[i], arr[j]) is said to be valid if func( arr[i] ) + func( arr[j] ) = func( XOR(arr[i], arr[j]) ) where func(x) returns the number of set bits in x.

Examples:

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Input: arr[] = {2, 3, 4, 5, 6}
Output:
(2, 4), (2, 5) and (3, 4) are the only valid pairs.

Input: arr[] = {12, 13, 34, 25, 6}
Output:

Approach: Iterating every possible pair and check whether the pair satisfies the given condition. If the condition is satisfied then update count = count + 1. Print the count in the end.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `// Function to return the number``// of set bits in n``int` `setBits(``int` `n)``{``    ``int` `count = 0;` `    ``while` `(n) {``        ``n = n & (n - 1);``        ``count++;``    ``}``    ``return` `count;``}` `// Function to return the count of required pairs``int` `countPairs(``int` `a[], ``int` `n)``{``    ``int` `count = 0;` `    ``for` `(``int` `i = 0; i < n - 1; i++) {` `        ``// Set bits for first element of the pair``        ``int` `setbits_x = setBits(a[i]);` `        ``for` `(``int` `j = i + 1; j < n; j++) {` `            ``// Set bits for second element of the pair``            ``int` `setbits_y = setBits(a[j]);` `            ``// Set bits of the resultant number which is``            ``// the XOR of both the elements of the pair``            ``int` `setbits_xor_xy = setBits(a[i] ^ a[j]);` `            ``// If the condition is satisfied``            ``if` `(setbits_x + setbits_y == setbits_xor_xy)` `                ``// Increment the count``                ``count++;``        ``}``    ``}` `    ``// Return the total count``    ``return` `count;``}` `// Driver code``int` `main()``{``    ``int` `a[] = { 2, 3, 4, 5, 6 };` `    ``int` `n = ``sizeof``(a) / ``sizeof``(a[0]);` `    ``cout << countPairs(a, n);``}`

## Java

 `// Java implementation of the approach``import` `java.io.*;` `class` `GFG``{``    ` `// Function to return the number``// of set bits in n``static` `int` `setBits(``int` `n)``{``    ``int` `count = ``0``;` `    ``while` `(n > ``0``)``    ``{``        ``n = n & (n - ``1``);``        ``count++;``    ``}``    ``return` `count;``}` `// Function to return the count of``// required pairs``static` `int` `countPairs(``int` `a[], ``int` `n)``{``    ``int` `count = ``0``;` `    ``for` `(``int` `i = ``0``; i < n - ``1``; i++)``    ``{` `        ``// Set bits for first element``        ``// of the pair``        ``int` `setbits_x = setBits(a[i]);` `        ``for` `(``int` `j = i + ``1``; j < n; j++)``        ``{` `            ``// Set bits for second element``            ``// of the pair``            ``int` `setbits_y = setBits(a[j]);` `            ``// Set bits of the resultant number which is``            ``// the XOR of both the elements of the pair``            ``int` `setbits_xor_xy = setBits(a[i] ^ a[j]);` `            ``// If the condition is satisfied``            ``if` `(setbits_x + setbits_y == setbits_xor_xy)` `                ``// Increment the count``                ``count++;``        ``}``    ``}` `    ``// Return the total count``    ``return` `count;``}` `    ``// Driver code``    ``public` `static` `void` `main (String[] args)``    ``{` `        ``int` `[]a = { ``2``, ``3``, ``4``, ``5``, ``6` `};``        ``int` `n = a.length;``        ``System.out.println(countPairs(a, n));``    ``}``}` `// This code is contributed by ajit.`

## Python3

 `# Python 3 implementation of the approach` `# Function to return the number``# of set bits in n``def` `setBits(n):``    ``count ``=` `0` `    ``while` `(n):``        ``n ``=` `n & (n ``-` `1``)``        ``count ``+``=` `1` `    ``return` `count` `# Function to return the count``# of required pairs``def` `countPairs(a, n):``    ``count ``=` `0` `    ``for` `i ``in` `range``(``0``, n ``-` `1``, ``1``):``        ` `        ``# Set bits for first element``        ``# of the pair``        ``setbits_x ``=` `setBits(a[i])` `        ``for` `j ``in` `range``(i ``+` `1``, n, ``1``):``            ` `            ``# Set bits for second element``            ``# of the pair``            ``setbits_y ``=` `setBits(a[j])` `            ``# Set bits of the resultant number``            ``# which is the XOR of both the``            ``# elements of the pair``            ``setbits_xor_xy ``=` `setBits(a[i] ^ a[j]);` `            ``# If the condition is satisfied``            ``if` `(setbits_x ``+``                ``setbits_y ``=``=` `setbits_xor_xy):``                ` `                ``# Increment the count``                ``count ``+``=` `1` `    ``# Return the total count``    ``return` `count` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``a ``=` `[``2``, ``3``, ``4``, ``5``, ``6``]` `    ``n ``=` `len``(a)``    ``print``(countPairs(a, n))` `# This code is contributed by``# Sanjit_Prasad`

## C#

 `// C# implementation of the approach``using` `System;``class` `GFG``{` `// Function to return the number``// of set bits in n``static` `int` `setBits(``int` `n)``{``    ``int` `count = 0;` `    ``while` `(n > 0)``    ``{``        ``n = n & (n - 1);``        ``count++;``    ``}``    ``return` `count;``}` `// Function to return the count of``// required pairs``static` `int` `countPairs(``int` `[]a, ``int` `n)``{``    ``int` `count = 0;` `    ``for` `(``int` `i = 0; i < n - 1; i++)``    ``{` `        ``// Set bits for first element``        ``// of the pair``        ``int` `setbits_x = setBits(a[i]);` `        ``for` `(``int` `j = i + 1; j < n; j++)``        ``{` `            ``// Set bits for second element``            ``// of the pair``            ``int` `setbits_y = setBits(a[j]);` `            ``// Set bits of the resultant number which is``            ``// the XOR of both the elements of the pair``            ``int` `setbits_xor_xy = setBits(a[i] ^ a[j]);` `            ``// If the condition is satisfied``            ``if` `(setbits_x + setbits_y == setbits_xor_xy)` `                ``// Increment the count``                ``count++;``        ``}``    ``}` `    ``// Return the total count``    ``return` `count;``}` `// Driver code``public` `static` `void` `Main()``{``    ``int` `[]a = { 2, 3, 4, 5, 6 };` `    ``int` `n = a.Length;` `    ``Console.Write(countPairs(a, n));``}``}` `// This code is contributed``// by Akanksha Rai`

## PHP

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## Javascript

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Output:
`3`

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