Leetcode - Add Binary

Given two binary strings, return their sum (also a binary string).

For example,
a = "11"
b = "1"
Return "100".

[Thoughts]:

public class Solution {
    public String addBinary(String a, String b) {
        int carry = 0;
        int p1    = a.length() - 1;
        int p2    = b.length() - 1;
        StringBuilder sb = new StringBuilder();
        
        while(p1>=0 || p2>=0 || carry>0){
            if(p1>=0)
              carry += a.charAt(p1--)-'0';
            if(p2 >=0)
              carry += b.charAt(p2--)-'0';
            sb.insert(0, carry%2);
            carry = carry/2;
              
        }
        
        return sb.toString();
    }
}