follow up: 换成八进制
public class Solution {
public String addBinary(String a, String b) {
StringBuilder res=new StringBuilder();
int i=a.length()-1,j=b.length()-1,carry=0;
while(i>=0||j>=0){
int sum=carry;
if(i>=0) sum+=a.charAt(i--)-'0';
if(j>=0) sum+=b.charAt(j--)-'0';
res.append(sum%2);
carry=sum/2;
}
if(carry!=0) res.append(carry);
return res.reverse().toString();
}
}
