题目链接

活动 - AcWing 本课程系统讲解常用算法与数据结构的应用方式与技巧。https://www.acwing.com/problem/content/1305/

题解

代码

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>using namespace std;typedef long long LL;const int N = 3;int n, m;void mul(int c[], int a[], int b[][N])
{int temp[N] = {0};for (int i = 0; i < N; i++)for (int j = 0; j < N; j++)temp[i] = (temp[i] + (LL)a[j] * b[j][i]) % m;memcpy(c, temp, sizeof temp);
}void mul(int c[][N], int a[][N], int b[][N])
{int temp[N][N] = {0};for (int i = 0; i < N; i++)for (int j = 0; j < N; j++)for (int k = 0; k < N; k++)temp[i][j] = (temp[i][j] + (LL)a[i][k] * b[k][j]) % m;memcpy(c, temp, sizeof temp);
}int main()
{cin >> n >> m;int f1[N] = {1, 1, 1};int a[N][N] = {{0, 1, 0},{1, 1, 1},{0, 0, 1}};n--;while (n){if (n & 1) mul(f1, f1, a);  // res = res * amul(a, a, a);  // a = a * an >>= 1;}cout << f1[2] << endl;return 0;
}

参考资料

1. AcWing算法提高课