sgu 118 Digital Root

题意：算式中结果的数字根。

先取两数的数字根再乘起来，和先乘起来再取数字根结果一样。因此化简式子。

#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cstring>
#include <map>
#include <queue>
#include <set>
#include <cassert>
using namespace std;
const double EPS=1e-8;
const int SZ=10030,INF=0x7FFFFFFF;
typedef long long lon;

lon work(lon x)
{
    lon res=0;
    for(;x;)
    {
        res+=x%10;
        x/=10;
    }
    return res<10?res:work(res);
}

int main()
{
    std::ios::sync_with_stdio(0);
    //freopen("d:\\1.txt","r",stdin);
    lon casenum;
    cin>>casenum;
    for(lon time=1;time<=casenum;++time)
    {
        lon n;
        cin>>n;
        vector<lon> vct(n);
        for(lon i=0;i<n;++i)
        {
            cin>>vct[i];
        }
        lon cur=1;
        for(lon i=vct.size()-1;i>=0;--i)
        {
            cur*=vct[i];
            cur=work(cur);
            if(i==0)break;
            cur+=1;
        }
        cout<<cur<<endl;
    }
    return 0;
}