class Solution { public: string addBinary(string a, string b) { reverse(a.begin(),a.end()); reverse(b.begin(),b.end()); if(a.size()>b.size()) swap(a,b); while(a.size()<b.size()) a+='0'; int add=0; for(int i=0;i<a.size();i++) { int sum=add+a[i]+b[i]-'0'-'0'; b[i]=sum%2+'0'; add=sum/2; } if(add) b+='1'; reverse(b.begin(),b.end()); return b; } };