35 lines
1.4 KiB
Markdown
35 lines
1.4 KiB
Markdown
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Write a function that takes an unsigned integer and returns the number of '1' bits it has (also known as the [Hamming weight](http://en.wikipedia.org/wiki/Hamming_weight)).
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**Note:**
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* 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.
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* In Java, the compiler represents the signed integers using [2's complement notation](https://en.wikipedia.org/wiki/Two%27s_complement). Therefore, in **Example 3**, the input represents the signed integer. `-3`.
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**Example 1:**
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Input: n = 00000000000000000000000000001011
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Output: 3
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Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.
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**Example 2:**
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Input: n = 00000000000000000000000010000000
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Output: 1
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Explanation: The input binary string 00000000000000000000000010000000 has a total of one '1' bit.
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**Example 3:**
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Input: n = 11111111111111111111111111111101
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Output: 31
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Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one '1' bits.
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**Constraints:**
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* The input must be a **binary string** of length `32`.
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**Follow up:** If this function is called many times, how would you optimize it?
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https://leetcode.com/problems/number-of-1-bits
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