leetcode67. 二进制求和

先将a,b逆置，然后再运算，最后再逆置即可。

class Solution {
public:
    string addBinary(string a, string b) {
        string ans;
        reverse(a.begin(),a.end());
        reverse(b.begin(),b.end());
        int carry=0,n=max(a.size(),b.size());
        for(int i=0;i<n;i++){
            carry+=i<a.size()?(a[i]=='1'):0;
            carry+=i<b.size()?(b[i]=='1'):0;
            ans.push_back((carry%2)?'1':'0');
            carry/=2;
        }
        if(carry)ans.push_back('1');
        reverse(ans.begin(),ans.end());
        return ans;
    }
};