[luogu] 斐波那契数列

https://www.luogu.org/problemnew/show/P1962

矩阵快速幂加速

#include <bits/stdc++.h>

using namespace std;

#define gc getchar()
#define LL long long

const LL mod = ;

LL n, s;

inline LL read(){
    LL x = ; char c = gc;
    while(c < '' || c > '') c = gc;
    while(c >= '' && c <= '') x = x *  + c - '', c = gc;
    return x;
}

struct Node{
    LL m[][];
    Node() { memset(m,,sizeof m);}
    void clear(){for(int i = ; i <= n; i ++) m[i][i] = ;}
};

Node operator *(Node a, Node b){
    Node ret;
    for(int i = ; i <= n; i ++)
        for(int j = ; j <= n; j ++)
            for(int k = ; k <= n; k ++)
                ret.m[i][j] = (ret.m[i][j] + a.m[i][k] * b.m[k][j]) % mod;
    return ret;
}

Node ksm(Node a, LL p){
    Node ret; ret.clear();
    while(p){
        if(p & ) ret = ret * a;
        a = a * a;
        p >>= ;
    }
    return ret;
}

int main()
{
     s = read();
    n = ;
    Node a, b;
    a.m[][] = ; a.m[][] = ; a.m[][] = ; a.m[][] = ;
    b.m[][] = ; b.m[][] = ;
    Node Ans;
    Ans = ksm(a, s - );
    Node answer = Ans * b;
    cout << answer.m[][];

    return ;
}