Question

Formatted question description: https://leetcode.ca/all/191.html

 191	Number of 1 Bits

 Write a function that takes an unsigned integer and returns the number of ’1' bits it has
 (also known as the Hamming weight).

 For example, the 32-bit integer ’11' has binary representation 00000000000000000000000000001011,
 so the function should return 3.

 Credits:
 Special thanks to @ts for adding this problem and creating all test cases.

 @tag-bit

Algorithm

Sum up &1 result.

Code

Java

public class Number_of_1_Bits {

    public static void main(String[] args) {
        Number_of_1_Bits out = new Number_of_1_Bits();

        Solution s = out.new Solution();

        System.out.println(s.hammingWeight(11));
    }

    public class Solution {
        // you need to treat n as an unsigned value
        public int hammingWeight(int n) {

            int count = 0;

            while (n > 0) {
                count += n & 1;

                n >>= 1;
            }
            return count;
        }
    }

    public class Solution_cheat {
        // you need to treat n as an unsigned value
        public int hammingWeight(int n) {
            return Integer.bitCount(n); // Returns the number of one-bits in the two's complement binary representation
        }
    }

    public class Solution_toBinaryString {
        // you need to treat n as an unsigned value
        public int hammingWeight(int n) {

            String binaryString = Integer.toBinaryString(n);

            int count = 0;
            for (int i = 0; i < binaryString.length(); i++) {
                if (binaryString.charAt(i) == '1') {
                    count++;
                }
            }

            return count;
        }
    }
}

// OJ: https://leetcode.com/problems/number-of-1-bits/
// Time: O(1)
// Space: O(1)
class Solution {
public:
    int hammingWeight(uint32_t n) {
        int ans = 0;
        for (; n; n -= (n & -n)) ++ans;
        return ans;
    }
};

class Solution(object):
  def hammingWeight(self, n):
    """
    :type n: int
    :rtype: int
    """
    ans = 0
    while n > 0:
      n -= (n & -n)
      ans += 1
    return ans

191 - Number of 1 Bits

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