hdu 5451 Best Solver 快速矩阵乘法 Fibonacci数列的循环节-优快云博客

本文链接：https://blog.youkuaiyun.com/firenet1/article/details/48662291

本文介绍了一种用于解决特定数学问题的高效算法，包括时间限制、内存限制、输入输出规范及示例。算法利用快速矩阵乘法与Fibonacci数列的循环节原理，简化了计算过程。通过实例演示了如何快速准确地计算给定表达式的整数部分取模运算结果。

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Best Solver

Time Limit: 1500/1000 MS (Java/Others) Memory Limit: 65535/102400 K (Java/Others)
Total Submission(s): 401 Accepted Submission(s): 212

Problem Description

The so-called best problem solver can easily solve this problem, with his/her childhood sweetheart.

It is known that

y=(5+26√)1+2x .
For a given integer

x (0≤x<232) and a given prime number

M (M≤46337) , print

[y]%M . (

[y] means the integer part of

y )

Input

An integer

T (1<T≤1000) , indicating there are

T test cases.
Following are

T lines, each containing two integers

x and

M , as introduced above.

Output

The output contains exactly

T lines.
Each line contains an integer representing

[y]%M .

Sample Input

Sample Output

  
   Case #1: 97
Case #2: 969
Case #3: 16537
Case #4: 969
Case #5: 40453
Case #6: 10211
Case #7: 17947

Source

2015 ACM/ICPC Asia Regional Shenyang Online

本题正解是：快速矩阵乘法+ Fibonacci数列的循环节

以下是队里某同学的方法：

首先(5+2sqrt(6))^n + (5-2sqrt(6))^n 是一个整数，且(5-2sqrt(6))^n < 1

所以 (5+2sqrt(6))^n + (5-2sqrt(6))^n = x + y sqrt(6) + x - ysqrt(6)

所以算出 (5+2sqrt(6))^n的整数部分x，答案就是2*x-1

中间过程可以用取模操作。

他的思路是：1+2^x ,把1提出来，最后乘上即可。

对于{(5+2sqrt(6))^（2^n)}^2 = (5+2sqrt(6))^（2^(n+1))

这个乘法是有循环结的。

可能循环节开始位置不是(5+2sqrt(6))所以，预处理即可。

找到循环节以后，取模，然后快速矩阵乘即可。看代码。

#include<iostream>
#include<cstring>
#include<algorithm>
#include<vector>
#include<cstdio>
using namespace std;
#define ll unsigned int
struct Node{
    int a,b,t;
    Node(){}
    Node(int _a,int _t){
        a = _a;
        t = _t;
    }
};
vector<Node> head[50000];
ll mod ;
struct Mat{
    ll a[2][2];
    Mat(){
        memset(a,0,sizeof(a));
    }
    Mat operator *(const Mat & b){
        Mat c;
        memset(c.a,0,sizeof(c.a));
        for(int i = 0;i < 2; i++)
            for(int j = 0;j < 2; j++)
                for(int k = 0;k < 2; k++)
                    c.a[i][j] = (c.a[i][j]+a[i][k]*b.a[k][j])%mod;
        return c;
    }
};

int main(){
    ll t,n,m,tt=1;
    scanf("%lld",&t);
    while(t--){
        scanf("%lld%lld",&n,&m);
        mod = m;
        for(int i = 0;i < m; i++)
            head[i].clear();
        Node a,b;
        Mat x,y;
        ll cnt = 1,be=0;
        x.a[0][0] = x.a[1][1] = 5%mod;
        x.a[0][1] = 12%mod;
        x.a[1][0] = 2%mod;
        y = x;
        for(;;cnt++){
            a.a = x.a[1][0];
            a.b = x.a[0][0];
            a.t = cnt;
            int flag = 1;
            for(int i = 0;i < head[a.b].size(); i++){
                if(head[a.b][i].a == a.a){
                    flag = 0;
                    be = head[a.b][i].t;
                 }
            }
            if(flag==0) break;
            head[a.b].push_back(a);
            x = x*x;
        }
        cnt = cnt - be;
        ll num = 0,ans;
        x = y;

        for(int i = 0;i < min(be,n); i++){
            x = x*x;
        }
        if(n > be){
            n -= be;
            cnt = n%cnt;
            for(int i = 0;i < cnt; i++)
                x = x*x;
        }
        x = y * x;
        ans = 2*x.a[0][0]-1;
        ans %= mod;
        printf("Case #%lld: %lld\n",tt++,ans);
    }
    return 0;
}

出题人的解法：（过后更新）