一、题目

 

二、代码

class Solution {
public:
    string addStrings(string num1, string num2) {
    int end1 = num1.size()-1;
    int end2 = num2.size()-1;
    int next=0;//进位
    string s;
    while(end1>=0 || end2>=0)
    {
        int x1 = end1>=0?num1[end1]-'0':0;
        int x2 = end2>=0?num2[end2]-'0':0;
        int ret = x1 + x2 +next;
        next = ret/10;
        int y = ret%10;
        s.insert(0,1,'0'+y);
        end1--;
        end2--;
    }

    if(next == 1)//像‘9’+‘1’这种情况，剩下一个进位
    {
        s.insert(0,1,'0'+next);
    }
    return s;
}
};