CareerCup

private static String negaBinary(int x) {
    StringBuilder sb = new StringBuilder();
    while (x != 0) {
      int rem = x % -2;
      x = x / -2;
      if (rem < 0) {
        rem += 2;
        x += 1;
      }
      sb.append(rem);
    }
    return sb.reverse().toString();
  }

It is very similar to transforming into 2-base but tricky case is when reminder is negative.
we just have to convert negative reminder into non-negative:
a=b*c + r, so if r <0 then we can do a=b*c + r +b-b=b*(c+1) + (r-b)
in our case b=-2

Can you explain more what do you mean ?

Is it not simple as take compliment and then add one.

may be it is better to use a XOR rather than add one?

#!/usr/bin/env python3                                                                                                                 

def negabase(number, base):
    if 0 == number:
        return '0'

    digits = list()
    while 0 != number:
        number, remainder = divmod(number, base)

        if remainder < 0:
            # N == b*q + (b - b) + r == b*(q + 1) + (r - b)                                                                            
            number, remainder = number + 1, remainder -	base
	
        digits.append(str(remainder))

    return ''.join(digits[::-1]) if len(digits) else '0'


def solution(number):
    return negabase(number, -2)


assert solution(-15) =='110001'
assert solution(10) ==  '11110'
assert solution(-5) == '1111'

package dir;

class result {

int reminder;
int result;

public result(int reminder, int result) {
this.reminder = reminder;
this.result = result;
}

public result() {
}

}

public class NewClass {

public NewClass() {
int num = 13;
int div = -2;
StringBuilder sb=new StringBuilder();
while (Math.abs(num) >0) {
result r = divide(num, div);
num = r.result;
//print(r);
sb.append(r.reminder);
}
sb.reverse();
System.out.println(sb);
}

void print(result r) {
System.out.println("result " + r.result + " reminder = " + r.reminder);
}

result divide(int num, int div) {
result r = new result();
//r.result = num % div;
int count = 0;
int reminder = 0;
if (num == 0 || div == 0) {
r.reminder = 0;
r.result = 0;
}

if (num > 0) {
if (div > 0) {
//later
} else {
while (num >= -div) {
num = num + div;
count++;
}

r.result = -count;
}
} else {
if (div > 0) {
//later
} else {
// both are negative
while (num < 0) {
num = num - div;
count++;
}

r.result = count;
}
}

r.reminder = num;
return r;
}

public static void main(String[] args) {
new NewClass();
}
}

1's complement and then 2's complement.