add-binary(AC).cpp

#include <algorithm>
using namespace std;

class Solution {
public:
    /**
     * @param a a number
     * @param b a number
     * @return the result
     */
    string addBinary(string& a, string& b) {
        if (a.length() < b.length()) {
            return addBinary(b, a);
        }
        
        reverse(a.begin(), a.end());
        reverse(b.begin(), b.end());
        
        string s = "";
        int al = a.length();
        int bl = b.length();
        int i;
        for (i = 0; i < bl; ++i) {
            s.push_back(a[i] + b[i] - '0');
        }
        for (i = bl; i < al; ++i) {
            s.push_back(a[i]);
        }
        
        int c = 0;
        for (i = 0; i < al - 1; ++i) {
            c = s[i] - '0' >> 1;
            s[i] = (s[i] - '0' & 1) + '0';
            s[i + 1] += c;
        }
        c = s[i] - '0' >> 1;
        s[i] = (s[i] - '0' & 1) + '0';
        if (c) {
            s.push_back('1');
        }
        reverse(s.begin(), s.end());
        
        return s;
    }
};