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1733.cpp
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1733.cpp
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#include<cstring>
#include<cstdio>
#include<queue>
char mp[30][30];
int cnt,ans,head[30000],gap[30000],dis[30000],sum,vi[30][30];
const int inf=1<<30;
struct EDGE
{
int to,f,nxt;
}edge[2000000];
int n,m,s,t,nn;
int dx[]={1,0,-1,0},dy[]={0,1,0,-1};
int di[][2]={1,0,-1,0,0,1,0,-1,0,0};
int min(int a,int b)
{
return a<b?a:b;
}
int in(int x,int y)
{
return x>=1&&x<=n&&y>=1&&y<=m&&mp[x][y]!='#';
}
void add(int a,int b,int c)
{
edge[cnt].to=b;
edge[cnt].f=c;
edge[cnt].nxt=head[a];
head[a]=cnt++;
edge[cnt].to=a;
edge[cnt].f=0;
edge[cnt].nxt=head[b];
head[b]=cnt++;
}
void init()
{
cnt=ans=sum=0;
memset(head,-1,sizeof(head));
for(int i=1;i<=n;i++)
scanf("%s",mp[i]+1);
s=1,t=2;
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)
{
int num=(i-1)*m+j+2;
if(mp[i][j]=='X')
{
sum++;
add(s,num,1);
}
}
nn=2+n*m;
}
int dfs(int x,int y)//DFSÑ°ÕÒÔö¹ã·
{
vi[x][y]=1;
if(mp[x][y]=='@')
return 1;
for(int i=0;i<4;i++)
{
int xx=x+dx[i];
int yy=y+dy[i];
if(!in(xx,yy))
continue;
if(vi[xx][yy])
continue;
if(dfs(xx,yy))
return 1;
}
return 0;
}
int fine()
{
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)
{
memset(vi,0,sizeof(vi));
if(mp[i][j]=='X'&&!dfs(i,j))
return 1;
}
return 0;
}
int gfs(int x,int flow)
{
if(x==t)
return flow;
int temp=flow,pos=nn-1,j;
for(j=head[x];j!=-1;j=edge[j].nxt)
{
int y=edge[j].to;
int c=edge[j].f;
if(c>0&&dis[x]==dis[y]+1)
{
int temp_flow=gfs(y,min(temp,c));
temp-=temp_flow;
edge[j].f-=temp_flow;
edge[j^1].f+=temp_flow;
if(temp==0||dis[s]==nn)
return flow-temp;
}
if(c>0&&pos>dis[y])
pos=dis[y];
}
if(temp==flow)
{
if(!(--gap[dis[x]]))
dis[s]=nn;
else
gap[dis[x]=pos+1]++;
}
return flow-temp;
}
int sap()
{
int maxflow=0;
memset(gap,0,sizeof(gap));
memset(dis,0,sizeof(dis));
gap[0]=nn;
while(dis[s]<nn)
{
maxflow+=gfs(s,inf);
}
return maxflow;
}
int judge(int ti)
{
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)
{
int u=(i-1)*m+j;
u=(ti-1)*m*n+2+u;
if(mp[i][j]=='#')
continue;
for(int k=0;k<5;k++)
{
int x=i+di[k][0];
int y=j+di[k][1];
int v=(x-1)*m+y;
v=ti*m*n+2+v;
if(!in(x,y))
continue;
add(u,v,1);
}
}
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)
{
int v=(i-1)*m+j;
v=2+ti*m*n+v;
if(mp[i][j]=='@')
{
add(v,t,1);
}
}
nn+=n*m;
ans+=sap();
return ans==sum;
}
int aws()
{
if(sum==0)
return 0;
int ti=0;
while(1)
{
ti++;
if(judge(ti))
break;
}
return ti;
}
int main()
{
while(2==scanf("%d%d",&n,&m))
{
init();
if(fine())
{
printf("-1\n");
continue;
}
printf("%d\n",aws());
}
return 0;
}