190. Reverse Bits - python3

Reverse bits of a given 32 bits unsigned integer.

Note:

• Note that in some languages such as Java, there is no unsigned integer type. In this case, both input and output will be given as a signed integer type. They 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 2 above, the input represents the signed integer -3 and the output represents the signed integer -1073741825.
  Follow up:

If this function is called many times, how would you optimize it?

처음 생각한 것: 2진수를 그대로 리스트로 만들어서 reverse() 해주자
=> 안됨

학창시절에도 bit 연산은 제대로 배운적이 없으므로 머리를 쓸 수 없어 힘을 빌렸다.

Other Answer 1:

class Solution:
    def reverseBits(self, n: int) -> int:
        ret, power = 0, 31
        while n:
            ret += (n & 1) << power
            n = n >> 1
            power -= 1
        return ret

32 비트이므로

ret += (n & 1) << power
: n 과 1 을 &(AND) 연산한 비트를 왼쪽으로 power 번 이동

n = n >> 1
: n 을 오른쪽으로 1 번 이동

...

n 을 계속 오른쪽으로 밀다보면 1은 모두 사라지고 0 이 됨 => return ret

xx....^!^