My Solution to Spotify's [Reversed Binary Numbers](https://www.spotify.com/us/jobs/tech/reversed-binary/) problem that's apparently wrong for reasons unknown to me. -_-

ReverseBinary.java

import java.util.Scanner;

/**
 * Class that contains logic to reverse the bits of an integer and spit it
 * back out.
 */
public class ReverseBinary {

  /**
   * Reverse the bits of an integer between 1 ≤ n ≤ 1000000000.
   *    i.e. 11 (1011) becomes 13 (1101)
   *
   * @param n The integer to reverse.
   * @return The reversed integer.
   */
  public static int reverseBits(int n) {
    // 1-indexed MSB Position
    int msbPosition = findMSBPosition(n);
    int reversed = 0;

    for (int i = 0; i < msbPosition; i++) {
      int mask = 1 << i;
      int bit = (n & mask) >> i;
      reversed |= (bit << (msbPosition - i - 1));
    }

    return reversed;
  }

  /**
   * Find the 1-indexed position of the MSB of a number.
   *    i.e. For the number 11 (1011), findMSBPosition() would return 4.
   *
   * @param n The number to find the MSB for.
   * @return The 1-indexed position of the MSB.
   * @protected
   */
  protected static int findMSBPosition(int n) {
    int msbPos = 0;
    int testNum = 1;
    while (testNum <= n) {
      msbPos++;
      testNum <<= 1;
    }

    return msbPos;
  }

  /**
   * Reads in a number and prints the bit-reversed number.
   *
   * @param args The arguments (which should just be one number).
   */
  public static void main(String[] args) {
    // Check valid args
    if (args.length != 1) {
      System.exit(0);
    }

    Scanner sc = new Scanner(args[0]);
    int n;
    if (!sc.hasNextInt()) {
      System.exit(0);
    }

    n = sc.nextInt();
    if (n < 1 || n > 1000000000) {
      System.exit(0);
    }

    System.out.println("" + reverseBits(n));
  }

}