0043.cpp

#include <string>
using namespace std;

static int x = []() {std::ios::sync_with_stdio(false); cin.tie(0); return 0; }();
class Solution 
{
public:
    string multiply(string num1, string num2) 
    {
        int m = num1.size(), n = num2.size();
        string res(m + n, '0');
        for (int i = m - 1; i >= 0; i--) 
        {
            for (int j = n - 1; j >= 0; j--) 
            {
                int sum = (num1[i] - '0') * (num2[j] - '0') + (res[i + j + 1] - '0');
                res[i + j + 1] = sum % 10 + '0';
                res[i + j] += sum / 10;
            }
        }
        for (int i = 0; i < m + n; i++) 
        {
            if (res[i] != '0') return res.substr(i);
        }
        return "0";
    }
};