题解 | 丛林木马

#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main() {
    int t;
    cin>>t;
    while(t--)
    {
        string s,ss;
        cin>>s>>ss;
        int ans=0;
        vector<int>sss;
        vector<int>ssss;
        int a=s.size();
        int b=ss.size();
        int t=0;
        for(int i=s.size()-1;i>=0;i--)
        {
           int x=(s[i]-'0')*b+t;
           t=x/10;
           x%=10;
           sss.push_back(x);
        }
        while(t)
        {
            sss.push_back(t%10);
            t/=10;
        }
        int tt=0;
        for(int i=ss.size()-1;i>=0;i--)
        {
           int xx=(ss[i]-'0')*a+tt;
           tt=xx/10;
           xx%=10;
           ssss.push_back(xx);
        }
        while(tt)
        {
            ssss.push_back(tt%10);
            tt/=10;
        }
        vector<int>o;
        if(sss.size()>ssss.size())
        {
            while(sss.size()!=ssss.size())
            {
                ssss.push_back(0);
            }
        }
        if(sss.size()<ssss.size())
        {
            while(sss.size()!=ssss.size())
            {
                sss.push_back(0);
            }
        }
        int ttt=0;
        for(int i=0;i<sss.size();i++)
        {
          int xxx=sss[i]+ssss[i]+ttt;
          ttt=xxx/10;
          xxx%=10;
          o.push_back(xxx);
        }
        if(ttt!=0)o.push_back(ttt);
        for(int i=o.size()-1;i>=0;i--)
        {
            ans+=o[i];
            if(i!=0)ans*=10;
            ans%=998244353;
        }
        cout<<ans<<endl;
    }
}