LeetCode题解之Add Strings

1、题目描述
2、问题分析
直接按照加法运算规则运算即可，注意进位问题。
3、代码
 1 string addStrings(string num1, string num2) {
 2         if( num1.empty() ) return num2;
 3         if( num2.empty() ) return num1;
 4         
 5         string::reverse_iterator it1 = num1.rbegin() ;
 6         string::reverse_iterator it2 = num2.rbegin() ;
 7         string s ;
 8         int up = 0;
 9         while( it1 != num1.rend() && it2 != num2.rend() ){
10             int a = (*it1 - '0') + (*it2 - '0') + up ;
11             if( a < 10 ){
12                 s = std::to_string( a ) + s;
13                 up = 0;
14             }else{
15                 s = std::to_string( a - 10 ) + s;
16                 up = 1;
17             }
18             ++it1;
19             ++it2;
20         }
21         
22         while( it1 != num1.rend() ){
23             if( *it1 - '0' + up  < 10 ){
24                 s = std::to_string( *it1 - '0' + up )  + s;
25                 up = 0;
26             }else{
27                 s = std::to_string( *it1 - '0' + up - 10 )  + s;
28                 up = 1;
29             }
30             ++it1;
31         }
32         
33         while( it2 != num2.rend() ){
34             if( *it2 - '0' + up < 10 ){
35                 s = std::to_string( *it2 - '0' + up ) + s;
36                 up = 0;
37             }else{
38                 s = std::to_string( *it2 - '0' + up - 10 ) + s;
39                 up = 1;
40             }
41             ++it2 ;
42         }
43         
44         if( up == 1 ){
45             s  = std::to_string(1) + s;
46         }
47         
48         return s;
49         
50     }