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 = 0;
        while( it1 != num1.rend() && it2 != num2.rend() ){
            int a = (*it1 - '0') + (*it2 - '0') + up ;
            if( a < 10 ){
                s = std::to_string( a ) + s;
                up = 0;
            }else{
                s = std::to_string( a - 10 ) + s;
                up = 1;
            }
            ++it1;
            ++it2;
        }
        
        while( it1 != num1.rend() ){
            if( *it1 - '0' + up  < 10 ){
                s = std::to_string( *it1 - '0' + up )  + s;
                up = 0;
            }else{
                s = std::to_string( *it1 - '0' + up - 10 )  + s;
                up = 1;
            }
            ++it1;
        }
        
        while( it2 != num2.rend() ){
            if( *it2 - '0' + up < 10 ){
                s = std::to_string( *it2 - '0' + up ) + s;
                up = 0;
            }else{
                s = std::to_string( *it2 - '0' + up - 10 ) + s;
                up = 1;
            }
            ++it2 ;
        }
        
        if( up == 1 ){
            s  = std::to_string(1) + s;
        }
        
        return s;
        
    }