Number of 1 Bits

Posted on Edited on In Views:

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, the input represents the signed integer. -3.

Example 1:

1
2
3
Input: n = 00000000000000000000000000001011
Output: 3
Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.

Example 2:

1
2
3
Input: n = 00000000000000000000000010000000
Output: 1
Explanation: The input binary string 00000000000000000000000010000000 has a total of one '1' bit.

Example 3:

1
2
3
Input: n = 11111111111111111111111111111101
Output: 31
Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one '1' bits.

位操作：

时间复杂度：O(logn)

空间复杂度：O(1)

1
2
3
4
5
6
7
8
9
10
11
class Solution {
public:
    int hammingWeight(uint32_t n) {
        int sum = 0;
        while (n!=0) {
            if ((n & 1) == 1)sum += 1;
            n >>= 1;
        }
        return sum;
    }
};

优化：

1
2
3
4
5
6
7
8
9
10
11
class Solution {
public:
    int hammingWeight(uint32_t n) {
        int ret = 0;
        while (n) {
            n &= n - 1;
            ret++;
        }
        return ret;
    }
};