# Count ways to generate pairs having Bitwise XOR and Bitwise AND equal to X and Y respectively

• Difficulty Level : Medium
• Last Updated : 13 Apr, 2021

Given two integers X and Y, the task is to find the total number of ways to generate a pair of integers A and B such that Bitwise XOR and Bitwise AND between A and B is X and Y respectively

Examples:

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Input: X = 2, Y = 5
Output: 2
Explanation:
The two possible pairs are (5, 7) and (7, 5).
Pair 1: (5, 7)
Bitwise AND = 5 & 7 = 2
Bitwise XOR = 5 ^ 7 = 5
Pair 2: (7, 5)
Bitwise AND = 7 & 5 = 2
Bitwise XOR = 7 ^ 5 = 5

Input: X = 7, Y = 5
Output: 0

Naive Approach: The simplest approach to solve the problem is to choose the maximum among X and Y and set all its bits and then check all possible pairs from 0 to that maximum number, say M. If for any pair of A and B, A & B and A⊕B becomes equal to X and Y respectively, then increment the count. Print the final value of count after checking for all possible pairs.
Time Complexity: O(M2)
Auxiliary Space: O(1)

Efficient Approach: The idea is to generate all possible combinations of bits at each position. There are 4 possibilities for the ith bit in X and Y which are as follows:

1. If Xi = 0 and Yi = 1, then Ai = 1 and Bi = 1.
2. If Xi = 1 and Yi = 1, then no possible bit assignment exist.
3. If Xi = 0 and Yi = 0 then Ai = 0 and Bi = 0.
4. If Xi = 1 and Yi = 0 then Ai = 0 and Bi = 1 or Ai = 1 and Bi = 0, where Ai, Bi, Xi, and Yi represent ith bit in each of them.

Follow the steps below to solve the problem:

1. Initialize the counter as 1.
2. For the ith bit, if Xi and Yi are equal to 1, then print 0.
3. If at ith bit, Xi is 1 and Yi is 0 then multiply the counter by 2 as there are 2 options.
4. After that, divide X and Y each time by 2.
5. Repeat the above steps for every ith bit until both of them become 0 and print the value of the counter.

Below is the implementation of the above approach:

## C++

 `// C++ program for the above approach` `#include ``using` `namespace` `std;` `// Function to return the count of``// possible pairs of A and B whose``// Bitwise XOR is X and Y respectively``int` `countOfPairs(``int` `x, ``int` `y)``{``    ``// Stores the count of pairs``    ``int` `counter = 1;` `    ``// Iterate till any bit are set``    ``while` `(x || y) {` `        ``// Extract i-th bit``        ``// of X and Y``        ``int` `bit1 = x % 2;``        ``int` `bit2 = y % 2;` `        ``// Divide X and Y by 2``        ``x >>= 1;``        ``y >>= 1;` `        ``// If Xi = 1 and Yi = 2,``        ``// multiply counter by 2``        ``if` `(bit1 == 1 and bit2 == 0) {` `            ``// Increase required count``            ``counter *= 2;``            ``continue``;``        ``}` `        ``// If Xi =1 and Yi = 1``        ``if` `(bit1 & bit2) {` `            ``// No answer exists``            ``counter = 0;``            ``break``;``        ``}``    ``}` `    ``// Return the final count``    ``return` `counter;``}` `// Driver Code``int` `main()``{``    ``// Given X and Y``    ``int` `X = 2, Y = 5;` `    ``// Function Call``    ``cout << countOfPairs(X, Y);` `    ``return` `0;``}`

## Java

 `// Java program for``// the above approach``import` `java.util.*;``class` `GFG{` `// Function to return the count of``// possible pairs of A and B whose``// Bitwise XOR is X and Y respectively``static` `int` `countOfPairs(``int` `x, ``int` `y)``{``  ``// Stores the count of pairs``  ``int` `counter = ``1``;` `  ``// Iterate till any bit are set``  ``while` `(x > ``0` `|| y > ``0``)``  ``{``    ``// Extract i-th bit``    ``// of X and Y``    ``int` `bit1 = x % ``2``;``    ``int` `bit2 = y % ``2``;` `    ``// Divide X and Y by 2``    ``x >>= ``1``;``    ``y >>= ``1``;` `    ``// If Xi = 1 and Yi = 2,``    ``// multiply counter by 2``    ``if` `(bit1 == ``1` `&& bit2 == ``0``)``    ``{``      ``// Increase required count``      ``counter *= ``2``;``      ``continue``;``    ``}` `    ``// If Xi =1 and Yi = 1``    ``if` `((bit1 & bit2) > ``0``)``    ``{``      ``// No answer exists``      ``counter = ``0``;``      ``break``;``    ``}``  ``}` `  ``// Return the final count``  ``return` `counter;``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``  ``// Given X and Y``  ``int` `X = ``2``, Y = ``5``;` `  ``// Function Call``  ``System.out.print(countOfPairs(X, Y));``}``}` `// This code is contributed by Princi Singh`

## Python3

 `# Python3 program for the above approach` `# Function to return the count of``# possible pairs of A and B whose``# Bitwise XOR is X and Y respectively``def` `countOfPairs(x, y):` `    ``# Stores the count of pairs``    ``counter ``=` `1` `    ``# Iterate till any bit are set``    ``while``(x ``or` `y):` `        ``# Extract i-th bit``        ``# of X and Y``        ``bit1 ``=` `x ``%` `2``        ``bit2 ``=` `y ``%` `2` `        ``# Divide X and Y by 2``        ``x >>``=` `1``        ``y >>``=` `1` `        ``# If Xi = 1 and Yi = 2,``        ``# multiply counter by 2``        ``if` `(bit1 ``=``=` `1` `and` `bit2 ``=``=` `0``):``            ` `            ``# Increase required count``            ``counter ``*``=` `2``            ``continue` `        ``# If Xi =1 and Yi = 1``        ``if``(bit1 & bit2):` `            ``# No answer exists``            ``counter ``=` `0``            ``break` `    ``# Return the final count``    ``return` `counter` `# Driver Code` `# Given X and Y``X ``=` `2``Y ``=` `5` `# Function call``print``(countOfPairs(X, Y))` `# This code is contributed by Shivam Singh`

## C#

 `// C# program for``// the above approach``using` `System;``class` `GFG{` `// Function to return the count of``// possible pairs of A and B whose``// Bitwise XOR is X and Y respectively``static` `int` `countOfPairs(``int` `x, ``int` `y)``{``  ``// Stores the count of pairs``  ``int` `counter = 1;` `  ``// Iterate till any bit are set``  ``while` `(x > 0 || y > 0)``  ``{``    ``// Extract i-th bit``    ``// of X and Y``    ``int` `bit1 = x % 2;``    ``int` `bit2 = y % 2;` `    ``// Divide X and Y by 2``    ``x >>= 1;``    ``y >>= 1;` `    ``// If Xi = 1 and Yi = 2,``    ``// multiply counter by 2``    ``if` `(bit1 == 1 && bit2 == 0)``    ``{``      ``// Increase required count``      ``counter *= 2;``      ``continue``;``    ``}` `    ``// If Xi =1 and Yi = 1``    ``if` `((bit1 & bit2) > 0)``    ``{``      ``// No answer exists``      ``counter = 0;``      ``break``;``    ``}``  ``}` `  ``// Return the readonly count``  ``return` `counter;``}` `// Driver Code``public` `static` `void` `Main(String[] args)``{``  ``// Given X and Y``  ``int` `X = 2, Y = 5;` `  ``// Function Call``  ``Console.Write(countOfPairs(X, Y));``}``}`` ` `// This code is contributed by Rajput-Ji`

## Javascript

 ``
Output:
`2`

Time Complexity: O(log M)
Auxiliary Space: O(1)

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