TLE，调过闭关

#include <bits/stdc++.h>
#define ll long long
using namespace std;
string a, b;
string add(string x, string y)
{
    if (x.size() < y.size()) swap(x, y);
    int p = x.size() - y.size();
    for (int i = 0; i <= p; i++) y = '0' + y;
    x = '0' + x;
    p = 0;
    for (int i = x.size() - 1; i >= 0; i--)
    {
        int tmp = x[i] + y[i] + p - '0' - '0';
        x[i] = tmp % 10 + '0';
        p = tmp / 10;
        // cout << (int)(x[i]) << endl;
    }
    if (x[0] == '0') x = x.substr(1);
    return x;
}
string sub(string x)
{
    for (int i = x.size() - 1; i >= 0; i--)
    {
        if (x[i] != '0')
        {
            x[i]--;
            for (int j = i + 1; j < x.size(); j++) x[j] = '9';
            break;
        }
    }
    for (int i = 0; i < x.size(); i++)
    {
        if (x[i] != '0') return x.substr(i);
    }
    return "0";
}
string mul(string x, string y)
{
    string ans = "0";
    while (y != "0")
    {
        y = sub(y);
        ans = add(ans, x);
    }
    return ans;
}
int main()
{
    // freopen(".in", "r", stdin);
    // freopen(".out", "w", stdout);
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    cin >> a >> b;
    cout << mul(a, b);
    return 0;
}