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

 string addStrings(string num1, string num2) {
         if( num1.empty() ) return num2;
         if( num2.empty() ) return num1;

         string::reverse_iterator it1 = num1.rbegin() ;
         string::reverse_iterator it2 = num2.rbegin() ;
         string s ;
         int up = ;
         while( it1 != num1.rend() && it2 != num2.rend() ){
             int a = (*it1 - '') + (*it2 - '') + up ;
             if( a <  ){
                 s = std::to_string( a ) + s;
                 up = ;
             }else{
                 s = std::to_string( a -  ) + s;
                 up = ;
             }
             ++it1;
             ++it2;
         }

         while( it1 != num1.rend() ){
             if( *it1 - '' + up  <  ){
                 s = std::to_string( *it1 - '' + up )  + s;
                 up = ;
             }else{
                 s = std::to_string( *it1 - '' + up -  )  + s;
                 up = ;
             }
             ++it1;
         }

         while( it2 != num2.rend() ){
             if( *it2 - '' + up <  ){
                 s = std::to_string( *it2 - '' + up ) + s;
                 up = ;
             }else{
                 s = std::to_string( *it2 - '' + up -  ) + s;
                 up = ;
             }
             ++it2 ;
         }

         if( up ==  ){
             s  = std::to_string() + s;
         }

         return s;

     }