Base-2 in Java

The challenge

In this challenge you must convert integers numbers from and to a negative-base binary system.

Negative-base systems can accommodate all the same numbers as standard place-value systems, but both positive and negative numbers are represented without the use of a minus sign (or, in computer representation, a sign bit); this advantage is countered by an increased complexity of arithmetic operations.

To help understand, the first eight digits (in decimal) of the Base(-2) system is:

[1, -2, 4, -8, 16, -32, 64, -128]

Example conversions:

Decimal, negabinary

6,   '11010'
-6,  '1110'
4,   '100'
18,  '10110'
-11, '110101'

The solution in Java code

Option 1:

public class Solution {
    
    public static String intToNegabinary(int i) {
        return Integer.toBinaryString((i+0xAAAAAAAA)^0xAAAAAAAA);
    }
    
    public static int negabinaryToInt(String s) {
        return s.chars().map(i->i-'0').reduce(0,(a,v)->v-2*a);
    }
    
}

Option 2:

public class Solution {

    public static String intToNegabinary(int i) {
        var sb = new StringBuilder();

        while (i != 0) {
            int remainder = Math.abs(i) % 2;
            sb.append(remainder);
            if (i < 0 && remainder > 0) i--;
            i /= -2;
        }
        var result = sb.reverse().toString();
        return result.isEmpty() ? "0" : result;
    }

    public static int negabinaryToInt(String s) {
        var strReversed = new StringBuilder(s).reverse();
        int result = 0;

        for (int i = 0; i < strReversed.length(); i++)
            if (strReversed.charAt(i) == '1')
                result += Math.pow(-2, i);

        return result;
    }
}

Option 3:

public class Solution {

  public static String intToNegabinary(int i) {
    return Integer.toUnsignedString(toNegabinary(i), 2);
  }

  public static int negabinaryToInt(String s) {
    return fromNegabinary(Integer.parseUnsignedInt(s, 2));
  }

  public static int toNegabinary(int i) {
    return (i + NEGATIVE_DIGITS) ^ NEGATIVE_DIGITS;
  }

  public static int fromNegabinary(int i) {
    return (i ^ NEGATIVE_DIGITS) - NEGATIVE_DIGITS;
  }

  private static final int NEGATIVE_DIGITS = 0xAAAAAAAA;

}

Test cases to validate our solution

import org.junit.Test;
import static org.junit.Assert.assertEquals;

public class SolutionTest {
    @Test
    public void testIntToNegabinary() {
        assertEquals("11010", Solution.intToNegabinary(6));
        assertEquals("1110", Solution.intToNegabinary(-6));
    }
    
    @Test
    public void testNegabinaryToInt() {
        assertEquals(6, Solution.negabinaryToInt("11010"));
        assertEquals(-6, Solution.negabinaryToInt("1110"));
    }
    
}
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