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:
Input: n = 00000000000000000000000000001011 Output: 3 Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.
Example 2:
Input: n = 00000000000000000000000010000000 Output: 1 Explanation: The input binary string 00000000000000000000000010000000 has a total of one '1' bit.
Example 3:
Input: n = 11111111111111111111111111111101 Output: 31 Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one '1' bits.
Constraints:
- The input must be a binary string of length
32
.
Follow up: If this function is called many times, how would you optimize it?
Solution: Bit Operation
Use n & 1 to get the lowest bit of n.
Use n >>= 1 to right shift n for 1 bit, e.g. removing the last bit.
Time complexity: O(logn)
Space complexity: O(1)
C++
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// Author: Huahua class Solution { public: int hammingWeight(uint32_t n) { int ans = 0; while (n) { ans += n & 1; n >>= 1; } return ans; } }; |
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