Leetcode_Add Binary

class Solution {public:    string addBinary(string a, string b) {        string s;int lenA=a.size();int lenB=b.size();if(lenA==0)return b;if(lenB==0)return a;if(lenA>lenB){b.insert(b.begin(),lenA-lenB,'0');}else{a.insert(a.begin(),lenB-lenA,'0');}int flag=0;for(int i=a.size()-1;i>=0;--i){int temp=a[i]-'0'+b[i]-'0'+flag;s.insert(s.begin(),temp%2+'0');flag=temp/2;}if(flag==1)s.insert(s.begin(),'1');return s;    }};