Given two binary strings, return their sum (also a binary string). http://www.leetcode.com/onlinejudge

leetcode_add_binary.cpp

#include <iostream>
#include <sstream>
#include <string>
using namespace std;

class Solution {
public:
    string addBinary(string a, string b) {
        stringstream ss(stringstream::in | stringstream::out);
        int addon = 0;
        int idx_a = a.length() - 1;
        int idx_b = b.length() - 1;
        while (idx_a >= 0 || idx_b >= 0) {
            if (idx_a >= 0) {
                addon += a[idx_a] - '0';
                idx_a--;
            }
            if (idx_b >= 0) {
                addon += b[idx_b] - '0';
                idx_b--;
            }
            ss << addon % 2;
            addon /= 2;
        }
        if (addon != 0) {
            ss << addon;
        }
        string ret;
        ss >> ret;
        reverse(ret.begin(), ret.end());
        return ret;
    }
};