hdu 2604 Queuing（矩阵快速幂乘法）

Queues and Priority Queues are data structures which are known to most computer scientists. The Queue occurs often in our daily life. There are many people lined up at the lunch time.

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<math.h>
#include<algorithm>
#include<queue>
#include<set>
#include<bitset>
#include<map>
#include<vector>
#include<stdlib.h>
#include <stack>
using namespace std;
#define PI acos(-1.0)
#define max(a,b) (a) > (b) ? (a) : (b)
#define min(a,b) (a) < (b) ? (a) : (b)
#define ll long long
#define eps 1e-10
#define MOD 1000000007
#define N 1000006
#define inf 1e12
int L,M;
struct Matrix{
int mp[4][4];
};
Matrix Mul(Matrix a,Matrix b){
Matrix res;
for(int i=0;i<4;i++){
for(int j=0;j<4;j++){
res.mp[i][j]=0;
for(int k=0;k<4;k++){
res.mp[i][j]=(res.mp[i][j]+(a.mp[i][k]*b.mp[k][j])%M+M)%M;
}
}
}
return res;
}
Matrix fastm(Matrix a,int b){
Matrix res;
memset(res.mp,0,sizeof(res.mp));
for(int i=0;i<4;i++){
res.mp[i][i]=1;
}
while(b){
if(b&1){
res=Mul(res,a);
}
a=Mul(a,a);
b>>=1;
}
return res;
}
int main()
{
while(scanf("%d%d",&L,&M)==2){

if(L==1){
printf("%d\n",2%M);
continue;
}
if(L==2){
printf("%d\n",2%M);
continue;
}
if(L==3){
printf("%d\n",6%M);
continue;
}
if(L==4){
printf("%d\n",9%M);
continue;
}

Matrix tmp;
for(int i=0;i<4;i++){
for(int j=0;j<4;j++){
tmp.mp[i][j]=0;
}
}

tmp.mp[0][0]=1;
tmp.mp[0][2]=1;
tmp.mp[0][3]=1;
tmp.mp[1][0]=1;
tmp.mp[2][1]=1;
tmp.mp[3][2]=1;
Matrix cnt=fastm(tmp,L-4);

Matrix g;
g.mp[0][0]=9;
g.mp[1][0]=6;
g.mp[2][0]=4;
g.mp[3][0]=2;
cnt=Mul(cnt,g);
printf("%d\n",cnt.mp[0][0]%M);
}

return 0;
}