Given two binary strings, return their sum (also a binary string).
For example,
a = "11"
b = "1"
Return "100".
此题主要考察数学知识，这里面注意，如果String的值要不断的改变的话，就最好用StringBuilder，我用了String结果没有通过，代码如下：
public class Solution {
public String addBinary(String a, String b) {
int i = a.length()-1;
int j = b.length()-1;
int c = 0;
String s = "";
while(i>=0||j>=0||c==1){
if(i>=0) c+=a.charAt(i--)-'0';
if(j>=0) c+=b.charAt(j--)-'0';
sb.append(c%2);
c/=2;
}
return sb.reverse().toString();
}
}