LeetCode题解之Multiply Strings

1、题目描述

2、问题分析

按照手算乘法的过程进行计算，首先计算乘法，然后计算加法。

3、代码

 string multiply(string num1, string num2) {
         string small ;
         string big;
         if( num1.size() < num2.size() ){
             small = num1;
             big = num2;
         }else if( num2.size() < num1.size() ){
             small = num2;
             big = num1;
         }else{
             small = num1;
             big = num2;
         }

         int n = small.size() ;
         vector<string> re;

         string::reverse_iterator it_s = small.rbegin() ;
         while( it_s != small.rend() ){
             string  s;
             int up = ;
             string::reverse_iterator it_b = big.rbegin() ;
             while( it_b != big.rend() ){
                 int m = (*it_s - '') * (*it_b - '') + up;
                 if(  m <  ){
                     s = std::to_string(m) + s;
                     up = ;
                 }else{
                     s = std::to_string( m% )  + s;
                     up = m/;
                 }
                 ++it_b;
             }
             if( up !=  ){
                 s = std::to_string( up ) + s;
             }
             re.push_back( s );
             ++it_s;
         }

         string zero;
         for( vector<string>::iterator it = re.begin() ; it != re.end() ; it++ ){
             *it += zero;
             zero += "";
         }

         string result = "" ;
         for( int i =  ; i < re.size() ; i++ ){
             result = binaryAdd( result , re[i] );
         }

         int q = ;
         for( string::iterator it = result.begin() ; it != result.end() ; ++it ){
             q += (*it - '');
         }
         if( q == )
             result = "";
         return result;

     }

     string binaryAdd( string s1 , string s2 ){
         string s;
         string::reverse_iterator it1 = s1.rbegin();
         string::reverse_iterator it2 = s2.rbegin();
         int up = ;
         while( it1 != s1.rend() && it2 != s2.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 != s1.rend() ){
             if( *it1 - '' + up <  ){
                 s = std::to_string( *it1 - '' + up ) + s;
                 up = ;
             }else{
                 s = std::to_string( *it1 - '' + up -  ) + s;
                 up = ;
             }
             ++it1;
         }

         while( it2 != s2.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;
     }