24. Reverse Bits

easyAsked at Ola

Reverse the bits of a 32-bit unsigned integer.

By Alex Chen, Founder, InterviewChamp.AI · Last verified 2026-05-20

Problem

Reverse the bits of a given 32-bit unsigned integer. Note that the result should be a 32-bit unsigned integer too.

Example 1

Input

n = 00000010100101000001111010011100

Output

964176192

Example 2

Input

n = 11111111111111111111111111111101

Output

3221225471

Convert to a 32-char binary string and reverse it.

const s = n.toString(2).padStart(32,'0');
return parseInt([...s].reverse().join(''),2);

Tradeoff:

For 32 iterations: shift result left, OR in the bottom bit of n, then shift n right. O(32) and O(1) space.

function reverseBits(n) {
  let r = 0;
  for (let i = 0; i < 32; i++) {
    r = (r << 1) | (n & 1);
    n >>>= 1;
  }
  return r >>> 0;
}

Tradeoff:

Ola checks if you reach for unsigned shift; tie it to flipping a compact 32-bit feature flag mask on a driver-app config payload.

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Output

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