1875: [SDOI2009]HH去散步 矩阵乘法

[code]#include<iostream>
#include<cstdio>
#include<cstring>
#define M 125
#define P 45989
using namespace std;
int n,m,t,a,b,cnt,sum;
int head[25];
int list[M],next[M],from[M];
inline int read()
{
    int a=0,f=1; char c=getchar();
    while (c<'0'||c>'9') {if (c=='-') f=-1; c=getchar();}
    while (c>='0'&&c<='9') {a=a*10+c-'0'; c=getchar();}
    return a*f;
}
struct Matrix
{
    int a[M][M];
    Matrix()
    {
        memset(a,0,sizeof(a));
    }
    friend Matrix operator*(Matrix a,Matrix b)
    {
        Matrix 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 Matrix operator^(Matrix a,int b)
    {
        Matrix 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;
    }
};
Matrix A,ans;
inline void insert(int x,int y)
{
    next[++cnt]=head[x];
    head[x]=cnt;
    from[cnt]=x;
    list[cnt]=y;
}
int main()
{
    n=read(); m=read(); t=read(); a=read()+1; b=read()+1;
    for (int i=1;i<=m;i++)
    {
        int u=read()+1,v=read()+1;
        insert(u,v); insert(v,u);
    }
    for (int i=head[a];i;i=next[i])
        ans.a[0][i]++;
    for (int i=1;i<=cnt;i++)
        for (int j=head[list[i]];j;j=next[j])
            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 (list[i]==b)
            (sum+=ans.a[0][i])%=P;
    cout << sum << endl;
    return 0;
}