Question：
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) {
StringBuffer sb = new StringBuffer();
String s1 = sb.append(a).reverse().toString();
sb.delete(0, sb.length());
String s2 = sb.append(b).reverse().toString();
sb.delete(0, sb.length());
char[] c1 = s1.toCharArray();
char[] c2 = s2.toCharArray();
int c1number = 0;
int c2number = 0;
int carry = 0;
int n = Math.max(c1.length, c2.length);
for (int i = 0; i < n; i++) {
if (i < c1.length) {
c1number = c1[i] - ‘0‘;
} else {
c1number = 0;
}
if (i < c2.length) {
c2number = c2[i] - ‘0‘;
} else {
c2number = 0;
}
int number = c1number + c2number + carry;
if (number > 1) {
sb.append(number - 2);
carry = 1;
} else {
sb.append(number);
carry = 0;
}
}
if (carry == 1) {
sb.append("1");
}
return sb.reverse().toString();
}
}