HDU 2256 Problem of Precision (Fast Power matrix)

Original link: http://www.cnblogs.com/lalalatianlalu/p/9733619.html

Title: it is the desire (sqrt (2) + sqrt (3)) ^ (2 * n) and then rounded down MOD1024

Thinking: This question is very interesting, but I think this question can only be the case, because this question can do is limit because this topic is very dead, we (sqrt (2) + sqrt (3)) into (5 + 2 * sqrt (6)) ^ n

Set Sn = An + bn, An = (5 + 2 * sqrt (6)) ^ n, Bn = (5-2 * sqrt (6)) ^ n, Bn can be found in less than 1, then we final answer Sn-1 is the modulo

We then constructed Sn * ((5 + 2 * sqrt (6)) + (5-2 * sqrt (6))), will continue to give simplified Sn * 10 = Sn + 1-Sn-1, and then quickly matrix power it

Code:

#include <cstdio>
using namespace std;
typedef long long LL;

const int MOD=1024;
///使用前要先对r,c赋值
struct mat{
    long long a[30][30];
    int r,c;
    mat operator *(const mat &b)const{
        mat ret;
        for (int i=0;i<r;i++){
            for (int j=0;j<b.c;j++){
                ret.a[i][j]=0;
                for (int k=0;k<c;k++)
                    ret.a[i][j]+=a[i][k]*b.a[k][j],ret.a[i][j]%=MOD;
            }
        }
        ret.r=r;
        ret.c=b.c;
        return ret;
    }
    void init_unit(int x)
    {
        r=c=x;
        for(int i=0;i<r;i++){
            for(int j=0;j<c;j++){
                if(i==j)a[i][j]=1;
                else a[i][j]=0;
            }
        }
    }
}unit;
mat qmod(mat p,LL n){
    unit.init_unit(p.c);
    mat ans=unit;
    while(n){
        if(n&1)ans=p*ans;
        p=p*p;
        n>>=1;
    }
    return ans;
}

int main()
{
    int T;
    scanf("%d",&T);
    while(T--){
        int n;
        scanf("%d",&n);
        mat A;
        A.r=2;A.c=2;
        A.a[0][0]=10;A.a[0][1]=-1;
        A.a[1][0]=1;A.a[1][1]=0;
        mat B;
        B.r=B.c=2;
        B.a[0][0]=10;
        B.a[1][0]=2;
        mat ans;
        ans.r=ans.c=2;
        ans=qmod(A,n-1);
        ans=ans*B;
        printf("%lld\n",(ans.a[0][0]+MOD-1)%MOD);
    }
    return 0;
}

 

Reproduced in: https: //www.cnblogs.com/lalalatianlalu/p/9733619.html