reverse-bits.ts

/**
 * 190. Reverse Bits  (Easy)
 * Link: https://leetcode.com/problems/reverse-bits/
 *
 * Reverse the bits of a given 32-bit unsigned integer.
 *
 * Example:
 *   Input:  n = 0b00000010100101000001111010011100
 *   Output:     0b00111001011110000010100101000000  (964176192)
 *
 * Approach:
 *   Build the result bit by bit: shift the result left, OR in the lowest bit of
 *   n, then shift n right. After 32 iterations the bits are mirrored. The final
 *   `>>> 0` reinterprets the result as an unsigned 32-bit value.
 *
 * Time:  O(32) = O(1)
 * Space: O(1)
 */
export function reverseBits(n: number): number {
  let result = 0;
  let value = n >>> 0;

  for (let i = 0; i < 32; i++) {
    result = (result << 1) | (value & 1);
    value >>>= 1;
  }

  return result >>> 0;
}