【字符串】415. 字符串相加

 1 class Solution {
 2 public:
 3     string addStrings(string num1, string num2) 
 4     {
 5         int la = num1.size();
 6         int lb = num2.size();
 7 
 8         string sum = la > lb ? num1 : num2;
 9 
10         int overflow = 0;
11 
12         for (int i = 0; i < sum.size(); i++)
13         {
14             char an = i < la ? num1[la - i - 1] : ‘0‘;
15             char bm = i < lb ? num2[lb - i - 1] : ‘0‘;
16             int bit = an - ‘0‘ + bm - ‘0‘ + overflow;
17             overflow = bit / 10;
18             sum[sum.size() - i - 1] = bit % 10 + ‘0‘;
19         }
20         if (overflow)
21         {
22             sum = ‘1‘ + sum;
23         }
24 
25         return sum;
26     }
27 };