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.

solution

We create an accumulator res and initialize it to 0, and then slowly build it up by adding the LSB of n, then left-shifting res. Then, we right-shift n to delete the current LSB and move the next one to the left over into the LSB position.

This way, the bits get reversed and we can return res.

def reverseBits(self, n: int) -> int:
	res = 0
	for _ in range(32):
		res <<= 1
		res += n & 1
	  
		n >>= 1
	return res