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# Minimum count of consecutive integers till N whose bitwise AND is 0 with N

• Difficulty Level : Easy
• Last Updated : 13 Sep, 2021

Given a positive integer N, the task is to print the minimum count of consecutive numbers less than N such that the bitwise AND of these consecutive elements, including integer N, is equal to 0.

Examples:

Input: N = 18
Output: 3
Explanation:
One possible way is to form a sequence of {15, 16, 17, and 18}. The bitwise AND of the given numbers is equal to 0.
Therefore, a minimum of 3 numbers are needed to make the bitwise AND of a sequence of 4 consecutive elements, including 18 to 0.

Input: N = 4
Output: 1
Explanation:
One possible way is to form a sequence of {4, 3}. The bitwise AND of the given numbers is equal to 0.
Therefore, a minimum of 1 number is needed to make the bitwise AND of a sequence of 2 consecutive elements including 4 to 0.

Naive Approach: The simplest approach is to iterate until N is greater than 0 and in each iteration check if the, bitwise AND of the numbers so far is equal to 0 or not. If not, then increase the count by 1.

Time Complexity: O(N)
Auxiliary Space: O(1)

Efficient Approach: The given problem can be solved based on the following observations:

1. To make the bitwise AND of sequence including N equal to 0, it is necessary to make the MSB bit of the number N equal to 0.
2. Therefore, the idea is to include all the integers greater than or equal to (2MSB -1) and less than N in the sequence, it will give the minimum count.

Follow the steps below to solve the problem:

Below is the implementation of the above approach:

## Java

 `// Java program for the above approach``class` `GFG``{``  ` `    ``// Function to count the minimum count of``    ``// integers such that bitwise AND of that``    ``// many consecutive elements is equal to 0``    ``static` `int` `count(``int` `N)``    ``{` `        ``// Stores the binary``        ``// representation of N``        ``String a = Integer.toBinaryString(N);` `        ``// Stores the MSB bit``        ``int` `m = a.length() - ``1``;``      ` `        ``// Stores the count``        ``// of numbers``        ``int` `res = (``int``) (N - (Math.pow(``2``, m) - ``1``));` `        ``// Return res``        ``return` `res;` `    ``}` `    ``// Driver Code``    ``public` `static` `void` `main(String[] args) {` `        ``// Given Input``        ``int` `N = ``18``;` `        ``// Function Call``        ``System.out.println(count(N));``    ``}``}` `// This code is contributed by shikhasingrajput`

## Python3

 `# Python program for the above approach` `# Function to count the minimum count of``# integers such that bitwise AND of that``# many consecutive elements is equal to 0`  `def` `count(N):` `    ``# Stores the binary``    ``# representation of N``    ``a ``=` `bin``(N)` `    ``# Excludes first two``    ``# characters "0b"``    ``a ``=` `a[``2``:]` `    ``# Stores the MSB bit``    ``m ``=` `len``(a)``-``1` `    ``# Stores the count``    ``# of numbers``    ``res ``=` `N ``-` `(``2``*``*``m``-``1``)` `    ``# Return res``    ``return` `res`  `# Driver Code``# Given Input``N ``=` `18` `# Function Call``print``(count(N))`

## C#

 `// C# program for the above approach``using` `System;``using` `System.Collections.Generic;``public` `class` `GFG``{``  ` `    ``// Function to count the minimum count of``    ``// integers such that bitwise AND of that``    ``// many consecutive elements is equal to 0``    ``static` `int` `count(``int` `N)``    ``{` `        ``// Stores the binary``        ``// representation of N``        ``String a = Convert.ToString(N, 2);` `        ``// Stores the MSB bit``        ``int` `m = a.Length - 1;``      ` `        ``// Stores the count``        ``// of numbers``        ``int` `res = (``int``) (N - (Math.Pow(2, m) - 1));` `        ``// Return res``        ``return` `res;` `    ``}` `    ``// Driver Code``    ``public` `static` `void` `Main(String[] args) {` `        ``// Given Input``        ``int` `N = 18;` `        ``// Function Call``        ``Console.WriteLine(count(N));``    ``}``}` `// This code is contributed by umadevi9616`

## Javascript

 ``
Output
`3`

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

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