Unset bits in the given range

2.3

Given a non-negative number n and two values l and r. The problem is to unset the bits in the range l to r in the binary representation of n, i.e, to unset bits from the rightmost lth bit to the rightmost rth bit.

Constraint: 1 <= l <= r <= number of bits in the binary representation of n.

Examples:

Input : n = 42, l = 2, r = 5
Output : 32
(42)10 = (101010)2
(32)10 = (100000)2
The bits in the range 2 to 5 in the binary
representation of 42 have been unset.

Input : n = 63, l = 1, r = 4
Output : 48

Approach: Following are the steps:

  1. Calculate num = (1 << (sizeof(int) * 8 – 1)) – 1. This will produce the highest positive integer num. All the bits in num will be set.
  2. Toggle bits in the range l to r in num. Refer this post.
  3. Now, perform n = n & num. This will unset the bits in the range l to r in n.
  4. Return n.

Note: The sizeof(int) has been used as input is of int data type. For large inputs you can use long int or long long int datatypes in place of int.

C/C++

// C++ implementation to unset bits in the given range
#include <bits/stdc++.h>

using namespace std;

// function to toggle bits in the given range
unsigned int toggleBitsFromLToR(unsigned int n,
                                unsigned int l,
                                unsigned int r)
{
    // calculating a number 'num' having 'r' number of bits
    // and bits in the range l to r are the only set bits
    int num = ((1 << r) - 1) ^ ((1 << (l - 1)) - 1);

    // toggle the bits in the range l to r in 'n'
    // and return the number
    return (n ^ num);
}

// function to unset bits in the given range
unsigned int unsetBitsInGivenRange(unsigned int n,
                                   unsigned int l, unsigned int r)
{
    // 'num' is the highest positive integer number
    // all the bits of 'num' are set
    unsigned int num = (1 << (sizeof(int) * 8 - 1)) - 1;

    // toggle the bits in the range l to r in 'num'
    num = toggleBitsFromLToR(num, l, r);

    // unset the bits in the range l to r in 'n'
    // and return the number
    return (n & num);
}

// Driver program to test above
int main()
{
    unsigned int n = 42;
    unsigned int l = 2, r = 5;
    cout << unsetBitsInGivenRange(n, l, r);
    return 0;
}

Java

// Java implementation to unset bits in the given range
import java.io.*;

class GFG 
{
    // Function to toggle bits in the given range
    static int toggleBitsFromLToR(int n, int l, int r)
    {
        // calculating a number 'num' having 'r' number of bits
        // and bits in the range l to r are the only set bits
        int num = ((1 << r) - 1) ^ ((1 << (l - 1)) - 1);
 
        // toggle the bits in the range l to r in 'n'
        // and return the number
        return (n ^ num);
    }
    
    // Function to unset bits in the given range
    static int unsetBitsInGivenRange(int n, int l, int r)
    {
        // 'num' is the highest positive integer number
        // all the bits of 'num' are set
        int num = (1 << (4 * 8 - 1)) - 1;
 
        // toggle the bits in the range l to r in 'num'
        num = toggleBitsFromLToR(num, l, r);
 
        // unset the bits in the range l to r in 'n'
        // and return the number
        return (n & num);
    }
    
    // driver program
	public static void main (String[] args) 
	{
		int n = 42;
        int l = 2, r = 5;
        System.out.println(unsetBitsInGivenRange(n, l, r));
	}
}

// Contributed by Pramod Kumar


Output:

32

This article is contributed by Ayush Jauhari. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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