1. Write a function (in any programming language) that gets an integer parameter and returns the number of 1 digits in its binary representation.

2. How would you implement this even faster if you had infinite memory and processing capabilities.

Question

1. Write a function (in any programming language) that gets an integer parameter and returns the number of 1 digits in its binary representation.

2. How would you implement this even faster if you had infinite memory and processing capabilities.

Anonymous · Accepted Answer

1.
using namespace std;

int countOnes(int n)
{
	int ret = 0;
	while (n > 0)
	{
		ret += (n & 1);
		n >>= 1;
	}
	return ret;
}

2. Store the answer in a table for all integers and look it up from there.

Anonymous · Answer

In Java, XOR the number with zer and then bits shift count the number of ones.

public class BitManipulation {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		findXORBits(6,0);

	}
	
	public static int findXORBits(int x, int y) {
		int bitCount = 0;
		int z= x^y;
		System.out.println(z);
		while (z != 0)
		{
		  //increment count if last binary digit is a 1:
		  bitCount += z & 1;
		  z = z >> 1;  //shift Z by 1 bit to the right
		}
		System.out.println(bitCount);
		
		return 0;
	}

}

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