LeetCode Top Interview 150
191. Number of 1 Bits
Easy
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
class Solution:
def hammingWeight(self, n: int) -> int:
sum_val = 0
flag = False
if n < 0:
flag = True
n = n - (1 << 31) # Equivalent to Integer.MIN_VALUE
while n > 0:
k = n % 2
sum_val += k
n //= 2
return sum_val + 1 if flag else sum_val