【luogu P1962 斐波那契数列】 题解

题目链接：https://www.luogu.org/problemnew/show/P1962

给你篇dalao的blog自己看吧，把矩阵快速幂的板子一改就OK

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
struct Matrix{
    long long m[3][3];
}A,E,ans;
long long n,k, mod = 1000000007;
Matrix mul(Matrix A,Matrix B)
{
    Matrix C;
    for(int i = 1; i <= 2; i++)
        for(int j = 1; j <= 2; j++)
        {
            C.m[i][j] = 0;
            for(int k = 1; k <= 2; k++)
                C.m[i][j] = (C.m[i][j]+(A.m[i][k]*B.m[k][j]))%mod;    
        }
    return C;
}
Matrix fast(Matrix A, long long k)
{
    Matrix S = E;
    while(k)
    {
        if(k&1) S = mul(S,A);
        A = mul(A,A);
        k = k>>1;
    }
    return S;
}
int main(){
    
    scanf("%lld",&k);
    
    E.m[2][2] = 1;
    E.m[1][1] = 1;
    A.m[1][1] = 1;
    A.m[1][2] = 1;
    A.m[2][1] = 1;
    ans = fast(A,k);
        
    printf("%lld ",(ans.m[2][1])%mod);
    return 0;
}