hdu 4990 Reading comprehension (矩阵快速幂)

//f
=2*f[n-2]+f[n-1]+1
//矩阵快速幂
# include<stdio.h>
# include<string.h>
# include<algorithm>
# include<iostream>
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;
}