[leetcode]Multiply Strings

大数乘法..写的有点复杂...

class Solution {
public:

    string multiply(string num1, string num2) {
        int size1 = num1.size();
        int size2 = num2.size();
        vector<int> n1(size1,0);
        vector<int> n2(size2,0);
        vector<int> n3(size1+size2+2 , 0);
        
        reverse(num1.begin() , num1.end());
        reverse(num2.begin() , num2.end());
        
        for(int i = 0 ; i < size1 ; i++) {
            n1[i] = num1[i] - '0';
        }
        
        for(int i = 0 ; i < size2 ; i++) {
            n2[i] = num2[i] - '0';
        }
        
        for(int i = 0 ; i < size1 ; i++) {
            for(int j = 0 ; j < size2 ; j ++) {
                n3[j+i] += n1[i] * n2[j];
                n3[j+i+1] += n3[j+i] / 10;
                n3[j+i] %=  10;
            } 
        }
        stringstream ss;
        int rightmost = size1 + size2;
        while(rightmost >= 0 && n3[rightmost] == 0) rightmost --;
        
        for(int i = 0 ; i <= rightmost ; i ++)
            ss << n3[i];
        string ans = ss.str();
        reverse(ans.begin() , ans.end());
        if(ans == "") return "0";
        return ans;
        
    }
};