数学专项number_theory：UVa 10127

用简单的模运算从长度为1开始枚举即可。

#include <iostream>
#include <cstdio>
using namespace std;
int n;
int solve()
{
    int v=1;
    int cnt=1;
    while(v)
    {
        v=(long long)(v*10+1)%n;
        cnt++;
    }
    return cnt;
}
int main()
{
    freopen("in.txt","r",stdin);
    while(cin>>n)
    {
        cout<<solve()<<endl;
    }
    return 0;
}