bzoj 1875: [SDOI2009]HH去散步

颓废题2

一看就是从一个点可以推到下一个点，明显的矩阵乘法。注意不能往回走，可以把点对应成边就好了，1号点新对应一个0号边。

#include<bits/stdc++.h>
#define N 100005
#define M 10000005
#define LL long long
#define inf 0x3f3f3f3f
using namespace std;
inline int ra()
{
    int x=0,f=1; char ch=getchar();
    while (ch<'0' || ch>'9') {if (ch=='-') f=-1; ch=getchar();}
    while (ch>='0' && ch<='9') {x=x*10+ch-'0'; ch=getchar();}
    return x*f;
}
const int p=45989;
int head[155];
int n,m,t,a,b,sum,cnt;
struct Edge{
    int to,next;
}e[305];
struct Maxtri{
    int a[155][155];
    Maxtri(){
        memset(a,0,sizeof(a));
    }
    friend Maxtri operator * (Maxtri a, Maxtri b) 
    {
        Maxtri ans;
        for (int i=0; i<=cnt; i++)
            for (int j=0; j<=cnt; j++)
                for (int k=0; k<=cnt; k++)    
                    (ans.a[i][j]+=a.a[i][k]*b.a[k][j]%p)%=p;
        return ans;
    }
    friend Maxtri operator ^ (Maxtri a, int b)
    {
        Maxtri ans;
        for (int i=0; i<=cnt; i++) ans.a[i][i]=1;
        for (;b;b>>=1,a=a*a)
            if (b&1) ans=ans*a;
        return ans;
    }
};
Maxtri ans,A;
void insert(int x, int y){
    e[++cnt].next=head[x]; e[cnt].to=y; head[x]=cnt;
}
int main()
{
    n=ra(); m=ra(); t=ra(); a=ra()+1; b=ra()+1;
    for (int i=1; i<=m; i++)
    {
        int x=ra()+1,y=ra()+1;
        insert(x,y); insert(y,x);
    }
    for (int i=head[a];i;i=e[i].next)
        ans.a[0][i]++;
    for (int i=1; i<=cnt; i++)
        for (int j=head[e[i].to];j;j=e[j].next)
            if (j!=i+((i&1)?1:-1)) A.a[i][j]++;
    A=A^(t-1); ans=ans*A;
    for (int i=1; i<=cnt; i++)
        if (e[i].to==b)
            (sum+=ans.a[0][i])%=p;
    cout<<sum;
    return 0;
}