package Algorithms.string;

public class AddBinary {

public String addBinary(String a, String b) {

if (a == null || b == null) {

return null;

}

if (a.length() == 0) {

return b;

}

if (b.length() == 0) {

return a;

}

StringBuilder sb = new StringBuilder();

int p1 = a.length() - 1;

int p2 = b.length() - 1;

int carry = 0;

while (p1 >= 0 || p2 >= 0) {

int sum = carry;

if (p1 >= 0) {

sum += (a.charAt(p1) - '0');

}

if (p2 >= 0) {

sum += (b.charAt(p2) - '0');

}

char c = sum % 2 == 1 ? '1': '0';

sb.insert(0, c);

carry = sum / 2;

p1--;

p2--;

}

if (carry == 1) {

sb.insert(0, '1');

}

return sb.toString();

}

}