readme.md

190. Reverse Bits

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.

Example 1:

Input: n = 00000010100101000001111010011100 Output: 964176192 (00111001011110000010100101000000) Explanation: The input binary string 00000010100101000001111010011100 represents the unsigned integer 43261596, so return 964176192 which its binary representation is 00111001011110000010100101000000.

Example 2:

Input: n = 11111111111111111111111111111101 Output: 3221225471 (10111111111111111111111111111111) Explanation: The input binary string 11111111111111111111111111111101 represents the unsigned integer 4294967293, so return 3221225471 which its binary representation is 10111111111111111111111111111111.

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 reverseBits(self, n: int) -> int:
        result = 0  # This will hold the reversed bits
        for i in range(32):  # We need to handle all 32 bits
            # Shift result to the left to make room for the next bit
            result <<= 1
            # Add the least significant bit of n to result
            result |= n & 1
            # Shift n to the right to process the next bit in the next iteration
            n >>= 1
        return result

Thoughts

Time Complexity

O(1) - 32 bit fixed size

Space Complexity

O(1) - only result variable used