BZOJ2004: [Hnoi2010]Bus 公交线路

#include<cstring>
#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<queue>
#define rep(i,l,r) for (int i=l;i<=r;i++)
#define down(i,l,r) for (int i=l;i>=r;i--)
#define clr(x,y) memset(x,y,sizeof(x))
#define inf int(1e9)
#define maxn 20
#define mm 30031
using namespace std;
struct data{int a[205][205];
}ans,b;
int bin[maxn],v[maxn],n,k,p,cnt;
int read(){
    int x=0,f=1; char ch=getchar();
    while (!isdigit(ch)) {if (ch==‘-‘) f=-1; ch=getchar();}
    while (isdigit(ch)) {x=x*10+ch-‘0‘; ch=getchar();}
    return x*f;
}
int lowbit(int x){
    return (x&(-x));
}
void dfs(int dep,int s,int now){
    if (dep>k){
        v[++cnt]=s;
        return ;
    }
    down(i,now-1,1){
        dfs(dep+1,s+bin[i-1],i);
    }
}
void pre(){
    rep(i,1,cnt) rep(j,1,cnt){
        int x=(v[i]*2)^bin[p];
        x=x^v[j];
        if (x==lowbit(x)) b.a[i][j]=1;
    }
}
data operator *(data a,data b){
    data c; clr(c.a,0);
    rep(i,1,cnt) rep(j,1,cnt) rep(k,1,cnt){
        c.a[i][j]=(c.a[i][j]+(a.a[i][k]*b.a[k][j])%mm)%mm;
    }
    return c;
}
void pow(int x){
    rep(i,1,cnt) ans.a[i][i]=1;
    while (x){
        if (x&1) ans=ans*b;        
        b=b*b;
        x/=2;
    }
    printf("%d\n",ans.a[1][1]);
}
int main(){
    n=read(); k=read(); p=read();
    bin[0]=1; rep(i,1,p) bin[i]=bin[i-1]*2;
    dfs(2,bin[p-1],p);
    pre();
    pow(n-k);
    return 0;
}