hdu 4990 Reading comprehension (矩陣快速冪)

hdu 4990 Reading comprehension (矩陣快速冪)

//f[n]=2*f[n-2]+f[n-1]+1
//矩陣快速冪
# include
# include
# include
# include
using namespace std;
struct node
{
    __int64 m[3][3];
};
__int64 mod;
node answ,origin,d;
node f(node a,node b)
{
    __int64 i,j,k;
    node c;
    for(i=0; i<3; i++)
    {
        for(j=0; j<3; j++)
        {
            c.m[i][j]=0;
            for(k=0; k<3; k++)
            {
                c.m[i][j]+=(a.m[i][k]*b.m[k][j])%mod;
                c.m[i][j]%=mod;
            }
        }
    }
    return c;
}
node quick(node answ,node origin,__int64 n)
{
    while(n)
    {
        if(n%2)
            answ=f(answ,origin);
        origin=f(origin,origin);
        n/=2;
    }
    return answ;
}
int main()
{
    __int64 i,j,n;
    while(~scanf("%I64d %I64d",&n,&mod))
    {
        memset(answ.m,0,sizeof(answ.m));
        memset(d.m,0,sizeof(d.m));
        memset(origin.m,0,sizeof(origin.m));
        for(i=0; i<3; i++)
            answ.m[i][i]=1;
        d.m[0][0]=1;
        d.m[0][1]=2;
        d.m[0][2]=1;
        origin.m[0][1]=2;
        origin.m[1][0]=1;
        origin.m[1][1]=1;
        origin.m[2][1]=1;
        origin.m[2][2]=1;
        if(n==1)
            printf("%I64d\n",1%mod);
        else if(n==2)
            printf("%I64d\n",2%mod);
        else
        {

            answ=quick(answ,origin,n-2);
            answ=f(d,answ);
            printf("%I64d\n",answ.m[0][1]%mod);
        }
    }
    return 0;
}