Reverse Bits

The problem

Reverse bits of a given 32 bits unsigned integer.

Function: def reverseBits(n):

Example input (a JSON list of arguments): [43261596]
Expected output: 964176192

0 <= n < 2^32. Reverse exactly 32 bits, including leading zeroes.

Hints

1. Shift exactly 32 input bits into a new integer in reverse order.
2. Check the supplied examples, empty/boundary cases and the stated answer policy before optimizing.

Worked answer

Try it yourself first. When you are ready, open the answer below.

def reverseBits(n):
    out=0
    for _ in range(32):out=(out<<1)|(n&1);n>>=1
    return out

Why it works

Shift exactly 32 input bits into a new integer in reverse order. The fixed width matters because leading zero bits become trailing zero bits; input is an unsigned 32-bit integer.

Complexity: O(32) time / O(1) fixed-width space.

Time: O(32) time · Space: O(1) fixed-width space