51Nod 1126 求递推序列的第N项（矩阵快速幂）

 #include <iostream>
 #include <algorithm>
 #include <cmath>
 #define MOD 7
 #define N 2
 using namespace std;

 struct Matrix
 {
     long long v[N][N];
 };

 //矩阵间的乘法%m
 Matrix matrix_mul(Matrix A, Matrix B, long long m)
 {
     Matrix ans;

     for (int i = ; i < N; i++)
     {
         for (int j = ; j < N; j++)
         {
             ans.v[i][j] = ;
             for (int k = ; k < N; k++)
             {
                 ans.v[i][j] += (A.v[i][k] * B.v[k][j]) % m;
             }
             ans.v[i][j] %= m;
         }
     }
     return ans;
 }

 //矩阵快速幂c^n%m
 Matrix matrix_pow(Matrix C, long long n, long long m)
 {
     Matrix ans = { , , ,  };//e
     while (n)
     {
         if (n & )
             ans = matrix_mul(ans, C, m);
         C = matrix_mul(C, C, m);
         n >>= ;
     }
     return ans;
 }

 int main()
 {
     long long n;
     int a, b;
     cin >> a >> b >> n;
     Matrix temp1 = { (a%MOD + MOD) % MOD, (b%MOD + MOD) % MOD, ,  };
     Matrix temp2 = { , , ,  }; // temp2{f[2],0,f[1],0}!!!!!

     if (n < )
     {
         cout <<  << endl;
         return ;
     }
     Matrix res = matrix_pow(temp1, n - , MOD);
     res = matrix_mul(res, temp2, MOD);
     cout << res.v[][] << endl;
     return ;
 }