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191. Number of 1 Bits

Description

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?

Solutions

• Java
• C++
• Python
• Go
• TypeScript
• Javascript
• RenderScript

• 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;
      }
  }
  

• class Solution {
  public:
      int hammingWeight(uint32_t n) {
          int ans = 0;
          while (n) {
              n &= n - 1;
              ++ans;
          }
          return ans;
      }
  };
  

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

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

• function hammingWeight(n: number): number {
      let ans: number = 0;
      while (n !== 0) {
          ans++;
          n &= n - 1;
      }
      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
      }
  }
  
  

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