题目链接：

题目大意：给定f[1] = 1, f[2] = 1, f[n] = ((A*f[n-1]) + (B*f[n-2])) % 7, 求f[n]   (n最大100,000,000)

思路：f[n]显然都是小于7的，而f[n]又只与f[n-1]和f[n-2]有关，于是想到只有7*7种组合，一定可以找到循环节。

代码：  

#include #include #include using namespace std;int main(){    int vis[7][7];    int f[100];    int A,B,n;    while(cin>>A>>B>>n){        if (A + B + n == 0){            break;        }        int t1 = 0, t2 = 0;        memset(vis, 0, sizeof(vis));        memset(f, 0, sizeof(f));        int t = 2;        int p1 = 1, p2 = 1;        vis[1][1] = 1;        f[1] = f[2] = 1;        while(1){            int p3 = (A * p2 + B * p1) % 7;            p1 = p2;            p2 = p3;            if (!vis[p1][p2]){                vis[p1][p2] = t;                f[t] = p1;                t ++;            }            else{                t1 = vis[p1][p2];                t2 = t;                t ++;                break;            }        }        if (n < t1){            cout<