67. Add Binary

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Problem

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

The input strings are both non-empty and contains only characters 1 or 0.

Example 1:

Input: a = "11", b = "1"
Output: "100"

Example 2:

Input: a = "1010", b = "1011"
Output: "10101"

Code

class Solution {
    public String addBinary(String a, String b) {
        StringBuilder sb = new StringBuilder();
        int p1 = a.length() - 1;
        int p2 = b.length() - 1;

        int carry = 0;
        while(p1 >= 0 || p2 >= 0){
            int num1 = p1 >= 0 ? (a.charAt(p1) - '0') : 0;
            int num2 = p2 >= 0 ? (b.charAt(p2) - '0') : 0;

            int sum = num1 + num2 + carry;
            sb.insert(0, sum % 2);
            carry = sum / 2;

            p1--;
            p2--;
        }

        if(carry != 0){
            sb.insert(0, carry);
        }

        return sb.toString();
    }
}