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).

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 above, the input represents the signed integer. -3.

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

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

# @lc code=start
using LeetCode

function hamming_weight(n::UInt32)::Int
    count = 0
    while n > 0
        n &= n - 1
        count += 1
    end

    return count
end
# @lc code=end

hamming_weight (generic function with 1 method)

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