class Solution {public:    string multiply(string num1, string num2) {        reverse(num1.begin(),num1.end());        reverse(num2.begin(),num2.end());        if(num1.length() < num2.length()) swap(num1,num2);        string sum(num1.length()+num1.length()+1,‘0‘);        for(int i = 0 ;i < num2.length(); ++ i){            int carry = 0;            for(int j = 0 ; j < num1.length(); ++ j){                int tmp = (num1[j]-‘0‘)*(num2[i]-‘0‘)+carry;                carry = tmp/10;                tmp = tmp%10+(sum[i+j]-‘0‘);                sum[i+j] =‘0‘+tmp%10;                sum[i+j+1] = ‘0‘+(sum[i+j+1]-‘0‘ + tmp/10);            }            if(carry != 0){                int num = carry+(sum[i+num1.length()]-‘0‘);                sum[i+num1.length()] = ‘0‘+num%10;                if(num/10) sum[i+num1.length()+1] = ‘0‘+(sum[i+num1.length()+1]-‘0‘+num/10);            }        }        reverse(sum.begin(),sum.end());        int index = 0;        for(index = 0 ; index < sum.length(); ++ index){            if(sum[index]!=‘0‘) return string(sum.begin()+index, sum.end());        }        if(index == sum.length()) return "0";    }};