Contest1220/G1.cpp

#include<bits/stdc++.h>
using namespace std;
int a, b, n;
int flag[67] = {0}; //mod7 很有意思，最多有 7 * 7种情况吧，找循环结构
 
// 十位数是本位，个位数是上一位，方便操作
 
int f[100] = {0};
 
int main()
{
    while(scanf("%d%d%d", &a, &b, &n))
    {
        int Begin = 100;
        int length = 0;
        memset(flag, 0, sizeof(flag));
        memset(f, 0, sizeof(f));
        if(a == 0 && b == 0 && n == 0) break;
        f[1] = 1;
        f[2] = 1;
 
        for(int i = 3; i <= 100; i++)
        {
            if(i < Begin)
            {
                int ans = ((a * f[i - 1]+ b * f[i - 2]) % 7 )* 10 + f[i - 1];
                if(flag[ans] == 0)
                    flag[ans] = i;
                else
                {
                    Begin = flag[ans];
                    length = i - flag[ans];
                }
                f[i] = ans / 10;
            }
            else
                break;
        }
 
        if(n < Begin)
            printf("%d\n", f[n]);
        else
            printf("%d\n", f[(n - Begin) % length + Begin]);
    }
    return 0;
}