191 - Number of 1 Bits-优快云博客

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博客围绕LeetCode上计算无符号整数中'1'的位数（汉明重量）的问题展开。介绍了问题描述，给出示例，还提到部分语言无无符号整数类型但不影响实现，最后提出若函数被多次调用该如何优化的后续思考，并给出问题链接。

Problem

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

Example 1:

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

Example 2:

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

Example 3:

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

Note:

Note that in some languages such as Java, there is no unsigned integer type. In this case, the input will be given as signed integer type and should not affect your implementation, as the internal binary representation of the integer 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?

Code

class Solution {
public:
    int hammingWeight(uint32_t n) {
        int ret = 0, m = n;
        for (int i = 0; i < 32; ++i) {
            if ((m & 1 << i) != 0) {
                ret++;
            }
        }
        return ret;
    }
};