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Check whether K-th bit is set or not

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  • Difficulty Level : Easy
  • Last Updated : 12 Sep, 2022
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Given a number n, check if the Kth bit of n is set or not.

Examples: 

Input: n = 5, k = 1
Output: SET
Explanation: 5 is represented as 101 in binary and has its first bit set.

Input: n = 2, k = 3
Output: NOT SET
Explanation: 2 is represented as 10 in binary, all higher i.e. beyond MSB, bits are NOT SET.

Check whether the K-th bit is set or not Using Left Shift Operator:

To solve the problem follow the below idea:

  • Left shift given number 1 by k-1 to create a number that has only set bit as k-th bit.
    temp = 1 << (k-1)
  • If bitwise AND of n and temp is non-zero, then result is SET else result is NOT SET.

Dry run of the above approach:

Input: n = 75 and k = 4
temp = 1 << (k-1) = 1 << 3 = 8 
Binary Representation of temp = 0..00001000 
Binary Representation of n = 0..01001011 
Since bitwise AND of n and temp is non-zero, result is SET.

Below is the implementation of the above approach:

C++




// CPP program to check if k-th bit
// of a given number is set or not
#include <bits/stdc++.h>
using namespace std;
 
void isKthBitSet(int n, int k)
{
    if (n & (1 << (k - 1)))
        cout << "SET";
    else
        cout << "NOT SET";
}
 
// Driver code
int main()
{
    int n = 5, k = 1;
 
    // Function call
    isKthBitSet(n, k);
    return 0;
}


C




// C program to check if k-th bit
// of a given number is set or not
#include <stdio.h>
 
void isKthBitSet(int n, int k)
{
    if (n & (1 << (k - 1)))
        printf("SET");
    else
        printf("NOT SET");
}
 
// Driver code
int main()
{
    int n = 5, k = 1;
 
    // Function call
    isKthBitSet(n, k);
    return 0;
}
 
// this code is contributed by devendrasaluke


Java




// Java program to check if k-th bit
// of a given number is set or not
 
class Number {
    public static void isKthBitSet(int n, int k)
    {
        if ((n & (1 << (k - 1))) > 0)
            System.out.print("SET");
        else
            System.out.print("NOT SET");
    }
 
    // Driver code
    public static void main(String[] args)
    {
        int n = 5, k = 1;
 
        // Function call
        isKthBitSet(n, k);
    }
}
 
// This code is contributed by rishabh_jain


Python3




# Python3 code to check if k-th bit
# of a given number is set or not
 
 
def isKthBitSet(n, k):
    if n & (1 << (k - 1)):
        print("SET")
    else:
        print("NOT SET")
 
 
# Driver code
if __name__ == "__main__":
    n = 5
    k = 1
 
    # Function call
    isKthBitSet(n, k)
 
# This code is contributed by "Sharad_Bhardwaj".


C#




// C# program to check if k-th bit
// of a given number is set or not.
using System;
 
class GFG {
 
    public static void isKthBitSet(int n, int k)
    {
        if ((n & (1 << (k - 1))) > 0)
            Console.Write("SET");
        else
            Console.Write("NOT SET");
    }
 
    // Driver code
    public static void Main()
    {
        int n = 5, k = 1;
 
        // Function call
        isKthBitSet(n, k);
    }
}
 
// This code is contributed by nitin mittal.


PHP




<?php
// PHP program to check if
// k-th bit of a given
// number is set or not
function isKthBitSet($n, $k)
{
    if ($n & (1 << ($k - 1)))
        echo "SET";
    else
        echo "NOT SET";
}
 
// Driver code
$n = 5; $k = 1;
 
// Function call
isKthBitSet($n, $k);
 
// This code is contributed
// by akt_mit
?>


Javascript




<script>
    // Javascript program to check if k-th bit
    // of a given number is set or not.
     
    function isKthBitSet(n, k)
    {
        if ((n & (1 << (k - 1))) > 0)
            document.write("SET");
        else
            document.write("NOT SET");
    }
     
    let n = 5, k = 1;
   
      isKthBitSet(n, k);
                                 
</script>


Output

SET

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

Check whether the K-th bit is set or not Using Right Shift Operator:

To solve the problem follow the below idea:

If we right shift n by k-1, we get the last bit as 1 if the Kth bit is set else 0

Below is the implementation of the above approach:

C++




// CPP program to check if k-th bit
// of a given number is set or not using
// right shift operator.
#include <iostream>
using namespace std;
 
void isKthBitSet(int n, int k)
{
    if ((n >> (k - 1)) & 1)
        cout << "SET";
    else
        cout << "NOT SET";
}
 
// Driver code
int main()
{
    int n = 5, k = 1;
 
    // Function call
    isKthBitSet(n, k);
    return 0;
}


C




// C program to check if k-th bit
// of a given number is set or not using
// right shift operator.
#include <stdio.h>
 
void isKthBitSet(int n, int k)
{
    if ((n >> (k - 1)) & 1)
        printf("SET");
    else
        printf("NOT SET");
}
 
// Driver code
int main()
{
    int n = 5, k = 1;
 
    // Function call
    isKthBitSet(n, k);
    return 0;
}
// this code is contributed by devendrasolunke


Java




// Java program to check if
// k-th bit of a given number
// is set or not using right
// shift operator.
import java.io.*;
 
class GFG {
    static void isKthBitSet(int n, int k)
    {
        if (((n >> (k - 1)) & 1) > 0)
            System.out.println("SET");
        else
            System.out.println("NOT SET");
    }
 
    // Driver code
    public static void main(String[] args)
    {
        int n = 5, k = 1;
 
        // Function call
        isKthBitSet(n, k);
    }
}
 
// This code is contributed
// by ajit


Python3




# PHP program to check if k-th bit of
# a given number is set or not using
# right shift operator.
 
 
def isKthBitSet(n, k):
    if ((n >> (k - 1)) and 1):
        print("SET")
    else:
        print("NOT SET")
 
 
# Driver code
if __name__ == "__main__":
    n, k = 5, 1
 
    # Function call
    isKthBitSet(n, k)
 
# This code contributed by
# PrinciRaj1992


C#




// C# program to check if
// k-th bit of a given number
// is set or not using right
// shift operator
using System;
 
class GFG {
    static void isKthBitSet(int n, int k)
    {
        if (((n >> (k - 1)) & 1) > 0)
            Console.WriteLine("SET");
        else
            Console.WriteLine("NOT SET");
    }
 
    // Driver code
    static public void Main()
    {
        int n = 5, k = 1;
 
        // Function call
        isKthBitSet(n, k);
    }
}
 
// This code is contributed
// by ajit


PHP




<?php
// PHP program to check
// if k-th bit of a given
// number is set or not
// using right shift operator.
 
function isKthBitSet($n, $k)
{
    if (($n >> ($k - 1)) & 1)
        echo "SET";
    else
        echo "NOT SET";
}
 
// Driver code
$n = 5; $k = 1;
 
// Function call
isKthBitSet($n, $k);
 
// This code is contributed
// by akt_mit
?>


Javascript




<script>
 
// Javascript program to check if
// k-th bit of a given number
// is set or not using right
// shift operator.
 
function isKthBitSet(n, k)
{
    if (((n >> (k - 1)) &
               1) > 0)
        document.write("SET");
    else
        document.write("NOT SET");
}
 
// Driver Code
 
    let n = 5, k = 1;
    isKthBitSet(n, k);
 
// This code is contributed by sanjoy_62.
</script>


Output

SET

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

This article is contributed by SAKSHI TIWARI. If you like GeeksforGeeks(We know you do!) and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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