hdu2262

#include<iostream>#include<cstdio>#include<cmath>#include<algorithm>#include<cstring>#include<queue>#define eps 1e-8#define maxn 226using namespace std;char s[22][22];int n,m;int cnt;struct node{    int x,y;    node(){};    node(int xx,int yy){x=xx,y=yy;}};node st;int vis[22][22];int X[]={0,0,-1,1};int Y[]={-1,1,0,0};bool inmap(int x,int y){    if(0<=x&&x<n&&0<=y&&y<m) return true;    else return false;}bool bfs(){    int flag=0;    memset(vis,-1,sizeof(vis));    queue<node> q;    cnt=0;    vis[st.x][st.y]=cnt++;    q.push(st);    while(!q.empty())    {        node tmp=q.front();q.pop();        if(s[tmp.x][tmp.y]=='$') flag=1;        for(int i=0;i<4;i++)        {            node next=node(tmp.x+X[i],tmp.y+Y[i]);            if(!inmap(next.x,next.y)) continue;            else if(s[next.x][next.y]=='#') continue;            else if(vis[next.x][next.y]==-1)            {                vis[next.x][next.y]=cnt++;                q.push(next);            }        }    }    return flag;}double A[maxn][maxn];void build(){    memset(A,0,sizeof(A));    for(int i=0;i<n;i++)    {        for(int j=0;j<m;j++)        {            if(vis[i][j]==-1) continue;            else if(s[i][j]=='$')            {                A[vis[i][j]][vis[i][j]]=1;                A[vis[i][j]][cnt]=0;            }            else            {                int nn=0;                for(int k=0;k<4;k++)                {                    node next= node(i+X[k],j+Y[k]);                    if(!inmap(next.x,next.y)) continue;                    else if(vis[next.x][next.y]==-1) continue;                    else if(s[next.x][next.y]=='#') continue;                    else                    {                        A[vis[i][j]][vis[next.x][next.y]]=-1.0;                        nn++;                    }                }                A[vis[i][j]][vis[i][j]]=nn;                A[vis[i][j]][cnt]=nn;            }        }    }}int sgn(double x){    if(fabs(x)<eps) return 0;    else return x>0?1:-1;}bool gaosi(){    int i,j,r,c;    for(r=0,c=0;r<cnt&&c<cnt;r++,c++)    {        //找不是0的行        for(i=r;i<cnt;i++)        {            if(sgn(A[i][c])!=0) break;        }        if(i==cnt)        {            r--;continue;        }        //替换        if(i!=r)        {            for(j=c;j<=cnt;j++) swap(A[i][j],A[r][j]);        }        //消元        for(i=r+1;i<cnt;i++)        {            for(j=cnt;j>=c;j--)            {                A[i][j]-=A[r][j]/A[r][c]*A[i][c];            }        }    }    for(i=r;i<cnt;i++)    {        if(sgn(A[i][cnt]!=0)) return 1;//无解    }    if(r<cnt) return cnt-r;//有无穷解    //回溯    for(i=cnt-1;i>=0;i--)    {        for(j=cnt-1;j>i;j--)        {            A[i][cnt]-=A[i][j]*A[j][cnt];        }        A[i][cnt]/=A[i][i];        A[i][i]=1;    }    return 0;}int main(){    while(scanf("%d%d",&n,&m)!=EOF)    {        for(int i=0;i<n;i++)        {            scanf("%s",s[i]);            for(int j=0;j<m;j++)            {                if(s[i][j]=='@')                {st.x=i,st.y=j;}            }        }        if(!bfs())        {            printf("-1\n");            continue;        }        build();        if(gaosi()!=0)        {            printf("-1\n");        }        else        {            printf("%.6lf\n",A[0][cnt]);        }    }    return 0;}