# Kth smallest positive integer Y such that its sum with X is same as its bitwise OR with X

Given two positive integers **X **and** K**, the task is to find the **K ^{th}** smallest positive integer (

**Y**) such that the sum of

**X**and

**Y**is equal to Bitwise OR of

**X**and

**Y**, i.e.

**(X + Y = X | Y)**

**Examples:**

Input:X = 5, K = 1Output:2Explanation:

Consider the smallest number as 2. The sum of 2 and 5 is 2 + 5 = 7 and the Bitwise OR of 2 and 5 is 7.

Input:X = 5, K = 5Output:18

**Approach:** The given problem can be solved by below observation:

- Using the properties of bitwise operator on two numbers
**X**and**Y**:

(X + Y) = (X & Y) + (X | Y)

- Therefore, for the value of
**X + Y**to be same as**X | Y**, the value of**X & Y**must be**0**.

- Also, we know that for
**X & Y**to be 0, the position of set bits in X must be unset in Y, and the positions of unset bits of X can be either 0 or 1 in Y.

- Hence, to find Kth smallest positive number meeting above conditions, we can use combinations for the bit positions of Y that are unset in X.

To implement the above, iterate the binary representation of **X** from right to left, and at every iteration, consider the following cases:

- If the current bit of
**X**is 1, the corresponding bit in Y will be 0, to get (X & Y) as 0. - If the current bit of
**X**is 0 and rightmost bit of K is 1, the corresponding bit of Y will be 1. This means that two combinations at current bit in Y has been used – first 0 and then 1. Then divide**K**by 2 - If the current bit of
**X**is 0 and rightmost bit of K is 0, the corresponding bit of Y will be 0. This means that only one combination at current bit in Y has been used – 0. Then divide**K**by 2 - If
**K**becomes 0, break the loop, stating that the Kth number has been found.

Finally, print the decimal conversion of Y as the required answer.

Below is the implementation of the above approach:

## C++

`// C++ implementation for the above approach` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Function to calculate K-th smallest ` `// solution(Y) of equation X+Y = X|Y` `long` `long` `KthSolution(` `long` `long` `X,` ` ` `long` `long` `K)` `{` ` ` `// Initialize the variable` ` ` `// to store the answer` ` ` `long` `long` `ans = 0;` ` ` `for` `(` `int` `i = 0; i < 64; i++) {` ` ` ` ` `// The i-th bit of X is off` ` ` `if` `(!(X & (1LL << i))) {` ` ` ` ` `// The i-bit of K is on` ` ` `if` `(K & 1) {` ` ` `ans |= (1LL << i);` ` ` `}` ` ` ` ` `// Divide K by 2` ` ` `K >>= 1;` ` ` `// If K becomes 0 then break` ` ` `if` `(!K) {` ` ` `break` `;` ` ` `}` ` ` `}` ` ` `}` ` ` `return` `ans;` `}` `// Driver Code` `int` `main()` `{` ` ` `long` `long` `X = 10, K = 5;` ` ` `cout << KthSolution(X, K);` ` ` `return` `0;` `}` |

## Java

`/*package whatever //do not write package name here */` `import` `java.io.*;` `class` `GFG ` `{` ` ` ` ` `// Function to calculate K-th smallest` ` ` `// solution(Y) of equation X+Y = X|Y` ` ` `static` `long` `KthSolution(` `long` `X, ` `long` `K)` ` ` `{` ` ` ` ` `// Initialize the variable` ` ` `// to store the answer` ` ` `long` `ans = ` `0` `;` ` ` `for` `(` `int` `i = ` `0` `; i < ` `64` `; i++) {` ` ` `// The i-th bit of X is off` ` ` `if` `((X & (` `1` `<< i)) == ` `0` `) {` ` ` `// The i-bit of K is on` ` ` `if` `((K & ` `1` `) > ` `0` `) {` ` ` `ans |= (` `1` `<< i);` ` ` `}` ` ` `// Divide K by 2` ` ` `K >>= ` `1` `;` ` ` `// If K becomes 0 then break` ` ` `if` `(K == ` `0` `) {` ` ` `break` `;` ` ` `}` ` ` `}` ` ` `}` ` ` `return` `ans;` ` ` `}` ` ` ` ` `// Driver Code` ` ` `public` `static` `void` `main(String[] args)` ` ` `{` ` ` `long` `X = ` `10` `;` ` ` `long` `K = ` `5` `;` ` ` `System.out.println(KthSolution(X, K));` ` ` `}` `}` `// This code is contributed by maddler.` |

## Python3

`# Python Program to implement` `# the above approach` `# Function to calculate K-th smallest` `# solution(Y) of equation X+Y = X|Y` `def` `KthSolution(X, K):` ` ` ` ` `# Initialize the variable` ` ` `# to store the answer` ` ` `ans ` `=` `0` ` ` `for` `i ` `in` `range` `(` `64` `):` ` ` `# The i-th bit of X is off` ` ` `if` `not` `(X & (` `1` `<< i)):` ` ` `# The i-bit of K is on` ` ` `if` `(K & ` `1` `):` ` ` `ans |` `=` `(` `1` `<< i)` ` ` ` ` `# Divide K by 2` ` ` `K >>` `=` `1` ` ` `# If K becomes 0 then break` ` ` `if` `not` `K:` ` ` `break` ` ` ` ` `return` `ans` `# Driver Code` `X ` `=` `10` `K ` `=` `5` `print` `(KthSolution(X, K))` `# This code is contributed by Saurabh Jaiswal` |

## C#

`/*package whatever //do not write package name here */` `using` `System;` `public` `class` `GFG ` `{` ` ` ` ` `// Function to calculate K-th smallest` ` ` `// solution(Y) of equation X+Y = X|Y` ` ` `static` `long` `KthSolution(` `long` `X, ` `long` `K)` ` ` `{` ` ` ` ` `// Initialize the variable` ` ` `// to store the answer` ` ` `int` `ans = 0;` ` ` `for` `(` `int` `i = 0; i < 64; i++) {` ` ` `// The i-th bit of X is off` ` ` `if` `((X & (1 << i)) == 0) {` ` ` `// The i-bit of K is on` ` ` `if` `((K & 1) > 0) {` ` ` `ans |= (1 << i);` ` ` `}` ` ` `// Divide K by 2` ` ` `K >>= 1;` ` ` `// If K becomes 0 then break` ` ` `if` `(K == 0) {` ` ` `break` `;` ` ` `}` ` ` `}` ` ` `}` ` ` `return` `ans;` ` ` `}` ` ` ` ` `// Driver Code` ` ` `public` `static` `void` `Main(String[] args)` ` ` `{` ` ` `long` `X = 10;` ` ` `long` `K = 5;` ` ` `Console.WriteLine(KthSolution(X, K));` ` ` `}` `}` `// This code is contributed by Princi Singh` |

## Javascript

` ` `<script>` ` ` `// JavaScript Program to implement` ` ` `// the above approach` `// Function to calculate K-th smallest ` `// solution(Y) of equation X+Y = X|Y` `function` `KthSolution(X,K)` `{` ` ` `// Initialize the variable` ` ` `// to store the answer` ` ` `let ans = 0;` ` ` `for` `(let i = 0; i < 64; i++) {` ` ` ` ` `// The i-th bit of X is off` ` ` `if` `(!(X & (1 << i))) {` ` ` ` ` `// The i-bit of K is on` ` ` `if` `(K & 1) {` ` ` `ans |= (1 << i);` ` ` `}` ` ` ` ` `// Divide K by 2` ` ` `K >>= 1;` ` ` `// If K becomes 0 then break` ` ` `if` `(!K) {` ` ` `break` `;` ` ` `}` ` ` `}` ` ` `}` ` ` `return` `ans;` `}` `// Driver Code` ` ` `let X = 10, K = 5;` ` ` `document.write(KthSolution(X, K));` ` ` `// This code is contributed by Potta Lokesh` ` ` `</script>` |

**Output:**

17

**Time Complexity: **O(log(X))**Auxiliary Space: **O(1)