Leetcode No.67 二进制求和

class Solution {
    public String addBinary(String a, String b) {
        int len1=a.length();
        int len2=b.length();
        int carry=0;
        String rs="";
        int i=len1-1;
        int j=len2-1;
        while(i>=0||j>=0){
           int c1=0;
           if(i>=0){
               c1=Integer.parseInt(String.valueOf(a.charAt(i--)));
           }
           int c2=0;
           if(j>=0){
               c2=Integer.parseInt(String.valueOf(b.charAt(j--)));
           }
           int s=c1+c2+carry;
           carry=s/2;
           rs=s%2+rs;
        }
        if(carry==1){
            rs=carry+rs;
        }
        return rs;
    }
}

class Solution {
    public String addBinary(String a, String b) {
        StringBuffer ans = new StringBuffer();

        int n = Math.max(a.length(), b.length()), carry = 0;
        for (int i = 0; i < n; ++i) {
            carry += i < a.length() ? (a.charAt(a.length() - 1 - i) - '0') : 0;
            carry += i < b.length() ? (b.charAt(b.length() - 1 - i) - '0') : 0;
            ans.append((char) (carry % 2 + '0'));
            carry /= 2;
        }

        if (carry > 0) {
            ans.append('1');
        }
        ans.reverse();

        return ans.toString();
    }
}