最近事情比较多，耽误了。。。。。。

Given two binary strings a and b, return their sum as a binary string.

Example 1:

Input: a = "11", b = "1"
Output: "100"

Example 2:

Input: a = "1010", b = "1011"
Output: "10101"

Constraints:

• 1 <= a.length, b.length <= 104
• a and b consist only of '0' or '1' characters.
• Each string does not contain leading zeros except for the zero itself.

利用栈来计算。

class Solution {
public:
    string addBinary(string a, string b) {
        stack<char> ss1;
        stack<char> ss2;
        stack<char> res;
        for(char element:a){
            ss1.push(element);
        }
        for(char element:b){
            ss2.push(element);
        }
        int carry=0;
        int curent=0;
        int aa=0;
        int bb=0;      
        while(!ss1.empty() || !ss2.empty()){
            if(ss1.size()>0){
                aa=ss1.top()-'0';
                ss1.pop();
            }
            else{
                aa=0;
            }
            if(ss2.size()>0){
                bb=ss2.top()-'0';
                ss2.pop();
            }
            else{
                bb=0;
            }
            curent=(aa+bb+carry)%2;
            carry=(aa+bb+carry)/2;
            res.push((curent+'0'));
            curent=0; 
        }
        if(carry>0) res.push((carry+'0'));
        string resul="";
        while(res.size()>0){
            resul+=res.top();
            res.pop();
        }
        cout<<resul<<endl;
        return resul;
    }
};