Bit Manipulation - Reverse Bits

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

Input: n = 43261596 (binary: 00000010100101000001111010011100)
Output: 964176192 (binary: 00111001011110000010100101000000)
Explanation: The input's binary bits reversed gives the output.

Input: n = 4294967293 (binary: 11111111111111111111111111111101)
Output: 3221225471 (binary: 10111111111111111111111111111111)

Iterate 32 times. In each iteration, extract the lowest bit of n and shift it into the correct position in the result. Shift n right by 1 after each step.

Initialize result to 0.
For each of the 32 bit positions: left-shift result by 1, then OR with the current lowest bit of n.
Right-shift n by 1 to move to the next bit.
After 32 iterations, result holds the reversed bits.

public class Solution { public int reverseBits(int n) { int result = 0; for (int i = 0; i < 32; i++) { result = (result << 1) | (n & 1); n >>>= 1; // unsigned right shift } return result; } }

Complexity Analysis:

Time complexity: O(1) — always 32 iterations regardless of input.
Space complexity: O(1) — constant extra space.