Add Binary

Traverse backwards

class Solution {
public:
    string addBinary(string a, string b) {
        string res="";
        int c=0;
        int i=a.size()-1, j=b.size()-1;
        while (i>=0||j>=0||c) {
            int cur=c;
            if (i>=0) cur+=a[i]-'0';
            if (j>=0) cur+=b[j]-'0';
            c=cur/2;
            cur=cur%2;
            res.insert(0, 1, cur+'0');
            i--;
            j--;
        }
        return res;
    }
};