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BrianKernighanAlgorithm.java

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package Others;

import java.util.Scanner;

/**

* @author Nishita Aggarwal

* <p>

* Brian Kernighan’s Algorithm

* <p>

* algorithm to count the number of set bits in a given number

* <p>

* Subtraction of 1 from a number toggles all the bits (from right to left) till the rightmost set bit(including the

* rightmost set bit).

* So if we subtract a number by 1 and do bitwise & with itself i.e. (n & (n-1)), we unset the rightmost set bit.

* <p>

* If we do n & (n-1) in a loop and count the no of times loop executes we get the set bit count.

* <p>

* <p>

* Time Complexity: O(logn)

*/

public class BrianKernighanAlgorithm {

/**

* @param num: number in which we count the set bits

* @return int: Number of set bits

*/

static int countSetBits(int num) {

int cnt = 0;

while (num != 0) {

num = num & (num - 1);

cnt++;

}

return cnt;

}

/**

* @param args : command line arguments

*/

public static void main(String args[]) {

Scanner sc = new Scanner(System.in);

int num = sc.nextInt();

int setBitCount = countSetBits(num);

System.out.println(setBitCount);

sc.close();

}

}