leetcode-add binary

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) {
int idx1=a.length()-1,idx2=b.length()-1;
int carry=0;
StringBuffer result=new StringBuffer();
while(idx1>=0||idx2>=0||carry>0){
int sum=0;
sum+=carry;
if(idx1>=0){sum+=(a.charAt(idx1)-'0');idx1--;}
if(idx2>=0){sum+=(b.charAt(idx2)-'0');idx2--;}
carry=sum/2;
sum=sum%2;
result.append(sum); // this is char
}
return result.reverse().toString();

}
}

和两个数相加是相同的想法，都是由三个部分组成。然后注意的问题：
append 里面直接就把int变成char类型了。

出问题的：居然while中的idx2写成idx1了