POTD Solutions | 29 Oct’ 23 | Check whether K-th bit is set or not

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Welcome to the daily solutions of our PROBLEM OF THE DAY (POTD). We will discuss the entire problem step-by-step and work towards developing an optimized solution. This will not only help you brush up on your concepts of Bit Manipulation but will also help you build up problem-solving skills.

POTD 29 Oct Solution

POTD 29 October: Check whether K-th bit is set or not:

Given a number N and a bit number K, check if the K^th index bit of N is set or not. A bit is called set if it is 1. The position of set bit ‘1‘ should be indexed starting with 0 from the LSB side in the binary representation of the number.

Example:

Input: N = 4, K = 0
Output: No
Explanation: The binary representation of 4 is 100, in which the 0^th index bit from LSB is not set. So, return false.

Input: N = 4, K = 2
Output: Yes
Explanation: Binary representation of 4 is 100, in which 2^nd index bit from LSB is set. So, return true.

Check whether K-th bit is set or not using Bitwise Operator:

The idea is to use Left Shift (<<) Operator. Left shift number 1 by K to create a number that has only set bit as K-th bit and store that number in temp variable. If bitwise AND of N and temp is non-zero, then K-th bit is SET else K-th bit is NOT SET.

Follow the steps to solve the above problem:

• Create a variable temp.
• Left shift number 1 by K and store it in temp. Now temp will have only the K-th bit set.
• Perform Bitwise AND of temp and N:
  • If Bitwise AND comes out to be non-zero then the K-th bit of N is set and hence return true.
  • If Bitwise AND comes out to be zero then the K-th bit of N is not set and hence return false.

Below is the implementation of above approach:

C++

class Solution {
public:
    // Function to check if Kth bit is set or not.
    bool checkKthBit(int n, int k)
    {
        // Create a variable temp with the Kth bit set to 1.
        int temp = (1 << k);

        // Perform a bitwise AND operation between 'n' and
        // the temp. If the result is not 0, it means the
        // Kth bit is set, so return true.
        if ((n & temp) != 0)
            return true;
        else
            // If the Kth bit is not set, return false.
            return false;
    }
};

Java

class CheckBit
{
    // Function to check if Kth bit is set or not.
    static boolean checkKthBit(int n, int k)
    {
        // Create a variable temp with the Kth bit set to 1.
        int temp = (1 << k);

        // Perform a bitwise AND operation between 'n' and
        // the temp. If the result is not 0, it means the
        // Kth bit is set, so return true.
        if ((n & temp) != 0)
            return true;
        else
            // If the Kth bit is not set, return false.
            return false;
    }

}

Python3

class Solution:

    #Function to check if Kth bit is set or not.
    def checkKthBit(self, n,k):
         # Create a variable temp with the Kth bit set to 1.
        temp = (1 << k)

        # Perform a bitwise AND operation between 'n' and
        # the temp. If the result is not 0, it means the
        # Kth bit is set, so return True.
        if (n & temp) != 0:
            return True
        else:
            # If the Kth bit is not set, return False.
            return False

Time Complexity: O(1), Left shift, right shift operator takes O(1) time.
Auxiliary Space: O(1), We are not using any extra space.