https://leetcode.com/problems/adding-two-negabinary-numbers/

adding-two-negabinary-numbers.java

class Solution {
    public int[] addNegabinary(int[] arr1, int[] arr2) {
        List<Integer> list = new ArrayList<>();
        
        int pt1 = arr1.length - 1;
        int pt2 = arr2.length - 1;
        
        int carrier = 0;
        
        while(pt1 >= 0 || pt2 >= 0) {
            int num1 = pt1 >= 0 ? arr1[pt1] : 0;
            int num2 = pt2 >= 0 ? arr2[pt2] : 0;
            int sum = num1 + num2 + carrier;
            if (sum == -1) {
                sum = 1;
                carrier = 1;
            } else {
                carrier = - (sum / 2);
                sum %= 2;
            }
            list.add(sum);
            pt1 --;
            pt2 --;
        }
        
        while (carrier != 0) {
            int sum = carrier;
            if (sum == -1) {
                sum = 1;
                carrier = 1;
            } else {
                carrier = - (sum / 2);
                sum %= 2;
            }
            list.add(sum);
        }
        
        int idx = list.size() - 1;
        while(idx > 0 && list.get(idx) == 0) {
            idx--;
        }
        int[] result = new int[idx + 1];
        for (int i = 0; i <= idx; i++) {
            result[i] = list.get(idx - i);
        }
        return result;
    }
}