Leetcode 190. Reverse Bits

Problem

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.

Algorithm

Decompose into bits and reassemble.

Code

class Solution:
    def reverseBits(self, n: int) -> int:
        buf = []
        for i in range(32):
            buf.append(n%2)
            n = n // 2
        ans = 0
        for i in range(32):
            ans = ans * 2 + buf[i]
        return ans