package leetcode;
import java.lang.Math;
public class AddBinary {
public String addBinary(String a, String b) {
if (a == null || a.length() == 0)
return b;
if (b == null || b.length() == 0)
return a;
int i = a.length() - 1;
int j = b.length() - 1;
int carry = 0;
StringBuilder res = new StringBuilder();
while (i >= 0 && j >= 0) {
int digit = (int) (a.charAt(i) - '0' + b.charAt(j) - '0') + carry;
carry = digit / 2;
digit %= 2;
res.insert(0, digit);
i--;
j--;
}
while (i >= 0) {
int digit = (int) (a.charAt(i) - '0') + carry;
carry = digit / 2;
digit %= 2;
res.insert(0, digit);
i--;
}
while (j >= 0) {
int digit = (int) (b.charAt(j) - '0') + carry;
carry = digit / 2;
digit %= 2;
res.insert(0, digit);
j--;
}
if (carry > 0) {
res.insert(0, carry);
}
return res.toString();
}
}