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

// For example,

// a = "11"

// b = "1"

// Return "100"

public class Solution {

public String addBinary(String a, String b) {

StringBuilder result = new StringBuilder();

int carry = 0;

int i = a.length() - 1;

int j = b.length() - 1;

while(i >= 0 || j >= 0) {

int sum = carry;

if(i >= 0) sum += a.charAt(i--) - '0';

if(j >= 0) sum += b.charAt(j--) - '0';

result.append(sum % 2);

carry = sum / 2;

}

if(carry != 0) result.append(carry);

return result.reverse().toString();

}

}