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Math & Bits · 127Easy

Reverse Bits

Reverse the bits of a given 32-bit unsigned integer and return the result.

Constraints

  • The input is a 32-bit unsigned integer.

Examples

reverseBits(43261596)    ->  964176192
reverseBits(0)           ->  0
reverseBits(4294967293)  ->  3221225471
reverseBits(1)           ->  2147483648   // the lowest bit moves to the top
reverseBits(2147483648)  ->  1            // and back again
reverseBits(4294967295)  ->  4294967295   // all ones is its own reverse

Edge cases

  • Leading zeros matter — always process exactly 32 bits.
  • In JS, bitwise operations are signed.
  • FOLLOW-UP
  • Follow-up: how would you optimize for many repeated calls? (byte-level lookup table)
Show the target complexity (spoiler)
Naive
Converting to a binary string, reversing it, and parsing back works but allocates on
Target
O(32) time, O(1) space — shift the result left and push in the input's lowest bit, 32 times.

Solve it

By hand, in your editor. The runner checks answers and timing.

git clone https://github.com/sarmadkung/optimal-round
cd optimal-round
# open problems/12-math-bits/127-reverse-bits.js
./practice c 127
Open the file on GitHub ↗