Question

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

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

Note:

Note that in some languages, such as Java, there is no unsigned integer type. In this case, the input will be given as a signed integer type. It should not affect your implementation, as the integer's internal binary representation is the same, whether it is signed or unsigned.
In Java, the compiler represents the signed integers using 2's complement notation. Therefore, in Example 3, the input represents the signed integer. -3.

Example 1:

Input: n = 00000000000000000000000000001011
Output: 3
Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.

Example 2:

Input: n = 00000000000000000000000010000000
Output: 1
Explanation: The input binary string 00000000000000000000000010000000 has a total of one '1' bit.

Example 3:

Input: n = 11111111111111111111111111111101
Output: 31
Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one '1' bits.

Constraints:

The input must be a binary string of length 32.

Follow up: If this function is called many times, how would you optimize it?

Algorithm

Sum up &1 result.

Code

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;
        }
    }
}

############

public class Solution {
    // you need to treat n as an unsigned value
    public int hammingWeight(int n) {
        int ans = 0;
        while (n != 0) {
            n &= n - 1;
            ++ans;
        }
        return ans;
    }
}

// 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:
    def hammingWeight(self, n: int) -> int:
        ans = 0
        while n:
            n &= n - 1
            ans += 1
        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

func hammingWeight(num uint32) int {
	ans := 0
	for num != 0 {
		num &= num - 1
		ans++
	}
	return ans
}

/**
 * @param {number} n - a positive integer
 * @return {number}
 */
var hammingWeight = function (n) {
    let ans = 0;
    while (n) {
        n &= n - 1;
        ++ans;
    }
    return ans;
};

impl Solution {
    pub fn hammingWeight(n: u32) -> i32 {
        n.count_ones() as i32
    }
}

191 - Number of 1 Bits

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