【矩阵乘法】bzoj2326 [HNOI2011]数学作业

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#include<cstdio>
#include<iostream>
#include<vector>
using namespace std;
typedef long long ll;
typedef vector<ll> vec;
typedef vector<vec> mat;
ll n,MOD;
mat operator * (const mat &a,const mat &b)
{
	mat c(a.size(),vec(b[0].size()));
	for(int i=0;i<a.size();++i)
	  for(int j=0;j<b[0].size();++j)
	    for(int k=0;k<b.size();++k)
	      c[i][j]=(c[i][j]+(a[i][k]%MOD)*(b[k][j]%MOD)%MOD)%MOD;
	return c;
}
mat Quick_Pow(mat x,ll p)
{
	if(!p)
	  {
	  	mat t(3,vec(3));
	  	for(int i=0;i<3;++i) t[i][i]=1;
	  	return t;
	  }
	mat res=Quick_Pow(x,p>>1);
	res=res*res;
	if(p&1) res=res*x;
	return res;
}
int main()
{
	cin>>n>>MOD;
	ll now=10;
	mat base(3,vec(3));
	base[0][0]=now;
	base[0][1]=base[0][2]=base[1][1]=base[1][2]=base[2][2]=1;
	mat fir(3,vec(1));
	fir[2][0]=1;
	while(now<=n)
	  {
	  	mat kbase=Quick_Pow(base,now-now/10);
	  	fir=kbase*fir;
	  	now*=10;
	  	base[0][0]=now;
	  }
	mat kbase=Quick_Pow(base,n-now/10+1);
	fir=kbase*fir;
	cout<<fir[0][0]<<endl;
	return 0;
}