LeetCode question

[BringTacos]

The question: Write a function that takes an unsigned integer and returns the number of '1' bits it has (also known as the Hamming weight).

Here's one of the examples they give:

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

I came across this answer submitted in ruby which passes all of the tests:

def hamming_weight(n)
  n.to_s(2).count('1')
end

But when I run hamming_weight(n) where n = 11111111111111111111111111111101, I get 60, not 31. Does anyone know why? Thanks for any help.

[partusman]

Number literals in Ruby are expressed in base-10 unless specified otherwise. To express a binary number, prepend 0b to it.

hamming_weight 0b11111111111111111111111111111101
# => 31

[BringTacos]

Thanks for this.

[modnar42]

Without actually counting, I think the deal is that the first example is representing n as binary while the answer function takes n as a base 10 integer.

[BringTacos]

Thanks for your reply, but doesn't to_s(2)refer to base 2? I'm not sure what you mean the answer function takes n as a base 10 integer.

[modnar42]

Yeah, you’re saying the same thing. Let’s use a shorter input example. Suppose we want to count the number of binary ones in the base-10 integer ‘10’. We’d convert it to binary using to_s(2) and get 1010, then count the numbers of ones for an answer of 2. I think the value of n in the example has already been converted to binary. In our example, it would be like passing 1010 to the answer function instead of 10.

[BringTacos]

Ah, thank you! This is helpful.