[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.

找出二进制数中1的个数，利用n & (n - 1)求解即可。

class Solution {
public:
    int hammingWeight(uint32_t n) {
        int res = 0;
        while (n) {
            n &= (n - 1);
            res++;
        }
        return res;
    }
};
// 3 ms

 也可以用二进制数的最后一位&1，计算1的个数。然后把二进制数右移一位。直到n变为0。

class Solution {
public:
    int hammingWeight(uint32_t n) {
        int res = 0;
        while (n) {
            res += (n & 1);
            n >>= 1;
        }
        return res;
    }
};
// 3 ms