leetcode[43]Multiply Strings

Given two numbers represented as strings, return multiplication of the numbers as a string.
Note: The numbers can be arbitrarily large and are non-negative.

class Solution {

public:

string multiply(string num1, string num2) 

{

    if(num1=="0"||num2=="0")return "0";

    int len1=num1.size();

    int len2=num2.size();

    int *n1=new int[len1];

    int *n2=new int[len2];

    for (int i=0;i<len1;i++)

    {

        n1[i]=num1[i]-'0';

    }

    for (int i=0;i<len2;i++)

    {

        n2[i]=num2[i]-'0';

    }

    int *res=new int[len1+len2];

    memset(res,0,(len1+len2)*sizeof(int));

    for (int i=len1-1;i>=0;i--)

    {

        for (int j=len2-1;j>=0;j--)

        {

            res[i+j+1]+=n1[i]*n2[j];

        }

    }

    string result="";

    for (int k=len1+len2-1;k>=0;k--)

    {

        if(k>0) res[k-1]+=res[k]/10;

        res[k]%=10;

        result=char(res[k]+'0')+result;

    }

    if(result[0]=='0')return result.substr(1,result.size());

    return result;

}

};