Leetcode: 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).

For example, the 32-bit integer ’11' has binary representation

00000000000000000000000000001011

, so the function should return 3

简单直观的解法。

class Solution {
public:
int hammingWeight(uint32_t n) {
int result = 0;
for (int i = 0; i < 32; ++i) {
if (n & 0x1) {
++result;
}
n >>= 1;
}

return result;
}
};

优化一下：

class Solution {
public:
int hammingWeight(uint32_t n) {
int result = 0;
while (n != 0) {
result += n & 0x1;
n >>= 1;
}

return result;
}
};

继续：

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

return result;
}
};