415. Add Strings

突然手癢想寫一下, 這邊要注意的就是carry,

這題我覺得算是string的入門題, 一定要熟練

class Solution {
public:
    string addStrings(string num1, string num2) {
        if(num1.size() > num2.size()){
            return addStrings(num2, num1);
        }
        int i = num1.size() - 1;
        int j = num2.size() - 1;
        int carry = 0;
        string res;
        
       while(i>=0 || j>=0 || carry){
        long sum = 0;
         if(i >= 0){sum += (num1[i] - '0');i--;}
         if(j >= 0){sum += (num2[j] - '0');j--;}
         sum += carry; 
         carry = sum / 10;
         sum = sum % 10;
         res =  to_string(sum) + res;
        }
   
        return res; 
    }
};