Number of 1 Bits Java

PROGRAM TO COUNT SET BITS IN AN INTEGER




class MAIN {

 

    // Lookup table

    static int[] BitsSetTable256 = new int[256];

 

    // Function to initialise the lookup table

    public static void initialize()

    {

 

        // To initially generate the

        // table algorithmically

        BitsSetTable256[0] = 0;

        for (int i = 0; i < 256; i++) {

            BitsSetTable256[i] = (i & 1) + BitsSetTable256[i / 2];

        }

    }

 

    // Function to return the count

    // of set bits in n

    public static int countSetBits(int n)

    {

        return (BitsSetTable256[n & 0xff]

                + BitsSetTable256[(n >> 8) & 0xff]

                + BitsSetTable256[(n >> 16) & 0xff]

                + BitsSetTable256[n >> 24]);

    }

 

    // Driver code

    public static void main(String[] args)

    {

 

        // Initialise the lookup table

        initialize();

        int n = 9;

        System.out.print(countSetBits(n));

    }

}




OUTPUT:

2

CREDITS: https://www.geeksforgeeks.org/count-set-bits-in-an-integer/