题目描述
Write a function that takes an unsigned integer and returns the number of ‘1’ bits it has (also known as the
Hamming weight
).
例子
例子 1
Input:
n = 00000000000000000000000000001011
Output:3
Explanation:The input binary string00000000000000000000000000001011
has a total of three'1'
bits.
例子 2
Input:
n = 00000000000000000000000010000000
Output:1
例子 3
Input:
n = 11111111111111111111111111111101
Output:31
Explanation:The input binary string11111111111111111111111111111101
has a total of thirty one'1'
bits.
Follow Up
- If this function is called many times, how would you optimize it?
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
.
Constraints
- The input must be a binary string of length
32
.
解题思路
简单的位操作即可,将数与 1 相与获取最低位的值并且不断将数字右移直至数字为 0 为止,代码如下:
#include <cstdint>
class Solution {
public:
int hammingWeight(uint32_t n) {
int count = 0;
while (n != 0) {
count += (n & 0x1);
n >>= 1;
}
return count;
}
};
- 时间复杂度:
O(1)
- 空间复杂度:
O(1)
GitHub 代码同步地址: 191.NumberOf1Bits.cpp
其他题目: GitHub: Leetcode-C++-Solution 博客: Leetcode-Solutions