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# Count pairs of elements such that number of set bits in their AND is B[i]

• Difficulty Level : Medium
• Last Updated : 26 Mar, 2021

Given two arrays A[] and B[] of N elements each. The task is to find the number of index pairs (i, j) such that i ≤ j and F(A[i] & A[j]) = B[j] where F(X) is the count of set bits in the binary representation of X.
Examples:

Input: A[] = {2, 3, 1, 4, 5}, B[] = {2, 2, 1, 4, 2}
Output:
All possible pairs are (3, 3), (3, 1), (1, 1) and (5, 5)
Input: A[] = {1, 2, 3, 4, 5}, B[] = {2, 2, 2, 2, 2}
Output:

Approach: Iterate through all the possible pairs (i, j) and check the count of set bits in their AND value. If the count is equal to B[j] then increment the count.
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `// Function to return the count of pairs``// which satisfy the given condition``int` `solve(``int` `A[], ``int` `B[], ``int` `n)``{``    ``int` `cnt = 0;` `    ``for` `(``int` `i = 0; i < n; i++)``        ``for` `(``int` `j = i; j < n; j++)` `            ``// Check if the count of set bits``            ``// in the AND value is B[j]``            ``if` `(__builtin_popcount(A[i] & A[j]) == B[j]) {``                ``cnt++;``            ``}` `    ``return` `cnt;``}` `// Driver code``int` `main()``{``    ``int` `A[] = { 2, 3, 1, 4, 5 };``    ``int` `B[] = { 2, 2, 1, 4, 2 };``    ``int` `size = ``sizeof``(A) / ``sizeof``(A[0]);` `    ``cout << solve(A, B, size);` `    ``return` `0;``}`

## Java

 `// Java implementation of the approach``public` `class` `GFG``{` `    ``// Function to return the count of pairs``    ``// which satisfy the given condition``    ``static` `int` `solve(``int` `A[], ``int` `B[], ``int` `n)``    ``{``        ``int` `cnt = ``0``;` `        ``for` `(``int` `i = ``0``; i < n; i++)``        ``{``            ``for` `(``int` `j = i; j < n; j++) ``// Check if the count of set bits``            ``// in the AND value is B[j]``            ``{``                ``if` `(Integer.bitCount(A[i] & A[j]) == B[j])``                ``{``                    ``cnt++;``                ``}``            ``}``        ``}` `        ``return` `cnt;``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `A[] = {``2``, ``3``, ``1``, ``4``, ``5``};``        ``int` `B[] = {``2``, ``2``, ``1``, ``4``, ``2``};``        ``int` `size = A.length;` `        ``System.out.println(solve(A, B, size));``    ``}``}` `/* This code contributed by PrinciRaj1992 */`

## Python3

 `# Python3 implementation of the approach` `# Function to return the count of pairs``# which satisfy the given condition``def` `solve(A, B, n) :``    ``cnt ``=` `0``;` `    ``for` `i ``in` `range``(n) :``        ``for` `j ``in` `range``(i, n) :` `            ``# Check if the count of set bits``            ``# in the AND value is B[j]``            ``c ``=` `A[i] & A[j]``            ``if` `(``bin``(c).count(``'1'``) ``=``=` `B[j]) :``                ``cnt ``+``=` `1``;``    ``return` `cnt;` `# Driver code``if` `__name__ ``=``=` `"__main__"` `:` `    ``A ``=` `[ ``2``, ``3``, ``1``, ``4``, ``5` `];``    ``B ``=` `[ ``2``, ``2``, ``1``, ``4``, ``2` `];``    ` `    ``size ``=` `len``(A);` `    ``print``(solve(A, B, size));` `# This code is contributed``# by AnkitRai01`

## C#

 `// C# Implementation of the above approach``using` `System;` `class` `GFG``{` `    ``// Function to return the count of pairs``    ``// which satisfy the given condition``    ``static` `int` `solve(``int` `[]A, ``int` `[]B, ``int` `n)``    ``{``        ``int` `cnt = 0;` `        ``for` `(``int` `i = 0; i < n; i++)``        ``{``            ``for` `(``int` `j = i; j < n; j++)``            ``// Check if the count of set bits``            ``// in the AND value is B[j]``            ``{``                ``if` `(countSetBits(A[i] & A[j]) == B[j])``                ``{``                    ``cnt++;``                ``}``            ``}``        ``}` `        ``return` `cnt;``    ``}``    ` `    ``// Function to get no of set``    ``// bits in binary representation``    ``// of positive integer n``    ``static` `int` `countSetBits(``int` `n)``    ``{``        ``int` `count = 0;``        ``while` `(n > 0)``        ``{``            ``count += n & 1;``            ``n >>= 1;``        ``}``        ``return` `count;``    ``}``    ` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``int` `[]A = {2, 3, 1, 4, 5};``        ``int` `[]B = {2, 2, 1, 4, 2};``        ``int` `size = A.Length;` `        ``Console.WriteLine(solve(A, B, size));``    ``}``}` `// This code is contributed by Princi Singh`

## Javascript

 ``
Output:
`4`

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