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Number of 1 Bits⚓︎

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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.

Solution⚓︎

Way 1⚓︎

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class Solution {
public:
    int hammingWeight(uint32_t n) {
        int res = 0;
        for (int i = 0; i < 32; i++) {
            if (n & 1 << i) res++;
        }
        return res;
    }
};
  • Time complexity: \(O(k)\), where \(k=32\);
  • Space complexity: \(O(1)\).

Way 2⚓︎

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class Solution {
public:
    int hammingWeight(uint32_t n) {
        int res = 0;
        while (n) {
            n = n & (n - 1);
            res++;
        }
        return res;
    }
};
  • Time complexity: \(O(\log n)\);
  • Space complexity: \(O(1)\).