BZOJ3270: 博物馆

#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<map>
#include<vector>
#define eps 1e-9
using namespace std;
int n,m,tot,aa,bb;
int d[405];
double a[405][405],p[405],f[405];
vector<int> e[405];
int id(int x,int y){return (x-1)*n+y;
}
void build(int x,int y)
{
    a[id(x,y)][id(x,y)]--;
    for (unsigned int i=0; i<e[x].size(); i++)
        for (unsigned int j=0; j<e[y].size(); j++)
        {
            int xx=e[x][i],yy=e[y][j];
            if (xx!=yy)
            {
                if (xx==x && yy==y) a[id(x,y)][id(xx,yy)]+=1.0*p[x]*p[y];
                else if (xx==x) a[id(x,y)][id(xx,yy)]+=1.0*p[xx]*(1-p[yy])/d[yy];
                else if (yy==y) a[id(x,y)][id(xx,yy)]+=1.0*(1-p[xx])*p[yy]/d[xx];
                else a[id(x,y)][id(xx,yy)]+=1.0*(1-p[xx])*(1-p[yy])/d[xx]/d[yy];
            }
        }
}
void gauss()
{
    double t; int to;
    for (int i=1; i<=tot; i++)
    {
        t=0,to=0;
        for (int j=i; j<=tot; j++) if (fabs(a[j][i])>t) t=fabs(a[j][i]),to=j;
        if (to!=i) for (int j=1; j<=tot+1; j++) swap(a[to][j],a[i][j]);
        for (int j=i+1; j<=tot; j++) 
        {
            if (fabs(a[j][i])<eps) continue;
            t=a[j][i]/a[i][i];
            for (int k=i; k<=tot+1; k++) a[j][k]-=t*a[i][k];
        }
    }
    for (int i=tot; i; i--)
    {
        t=1.0*a[i][tot+1];
        for (int j=i+1; j<=tot; j++) t-=1.0*f[j]*a[i][j];
        f[i]=1.0*t/a[i][i];
    }
}
void init()
{
    scanf("%d%d%d%d",&n,&m,&aa,&bb);
    tot=n*n;
    a[id(aa,bb)][tot+1]=-1;
    for (int i=1; i<=n; i++) e[i].push_back(i);
    for (int i=1; i<=m; i++)
    {
        int u,v; scanf("%d%d",&u,&v); d[u]++; d[v]++;
        e[u].push_back(v); e[v].push_back(u);
    }
    for (int i=1; i<=n; i++) scanf("%lf",&p[i]);
    for (int i=1; i<=n; i++) for (int j=1; j<=n; j++) build(i,j);
}
int main()
{
    init();
    gauss();
    for(int i=1;i<=n;i++)
    {
        int t=id(i,i);
        printf("%.6lf",f[t]);
        if(i!=n)printf(" ");
    }
    return 0;
}