Add Binary字符数字相加，字符串合成

class Solution {
public:
    string addBinary(string a, string b) {
        string longer=a.length()>b.length() ? a:b;
        string shorter=a.length()>b.length() ? b:a;
        int add=0;
        int j=longer.length()-1;
        for(int i=shorter.length()-1;i>=0;--i,--j){
            if(shorter[i]-‘0‘+longer[j]-‘0‘+add>1){
                longer[j]=‘0‘+(shorter[i]-‘0‘+longer[j]-‘0‘+add)%2;
                add=1;
            }else{
                longer[j]=‘0‘+(shorter[i]-‘0‘+longer[j]-‘0‘+add)%2;
                add=0;
            }
        }
        while(j>=0){
            if(longer[j]-‘0‘+add>1){
                longer[j]=‘0‘;
                add=1;
            }else{
                longer[j]=longer[j]+add;
                add=0;
            }
            --j;
        }
        if(add)
            longer.insert(0,1,‘1‘);
        return longer;
    }
};