CodeForces-450B Jzzhu and Sequences

#include <iostream>#include <cstdio>using namespace std;const int maxn = 8;const int INF = 1e9 + 7;int num[maxn];int x, y, n;int main(){    while(~scanf("%d %d", & x, & y))    {        num[1] = x % INF;        num[2] = y % INF;        num[3] = (y - x) % INF;        num[4] = - num[1];        num[5] = - num[2];        num[6] = - num[3];        cin >> n;        n %= 6;        if(n == 0)        {            if(num[6] < 0)                cout << INF + num[6] << endl;            else                cout << num[6] << endl;        }        else        {            if(num[n] < 0)                cout << INF + num[n] << endl;            else                cout << num[n] << endl;        }    }    return 0;}

题意：建一个序列。给出f1 = x, f2 = y 。fi = fi -1  + fi +1（都是下标）。之后再输入一个n。输出序列第n个数除以1000000007的余数。

题解：找规律水题。