http://blog.csdn.net/lxy767087094/article/details/68942422
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
const int dx[]={0,-1,0,1},dy[]={-1,0,1,0};
typedef long long ll;
const ll INF=10000000000000000ll;
#define MAXN 2505
#define MAXM 30005
int v[MAXM],en,first[MAXN],next[MAXM];
ll cap[MAXM];
int d[MAXN],cur[MAXN];
queue<int>q;
int S,T;
void Init_Dinic(){memset(first,-1,sizeof(first)); en=0;}
void AddEdge(const int &U,const int &V,const ll &W)
{
v[en]=V; cap[en]=W;
next[en]=first[U]; first[U]=en++;
v[en]=U; cap[en]=0;
next[en]=first[V]; first[V]=en++;
}
bool bfs()
{
memset(d,-1,sizeof(d)); q.push(S); d[S]=0;
while(!q.empty())
{
int U=q.front(); q.pop();
for(int i=first[U];i!=-1;i=next[i])
if(d[v[i]]==-1 && cap[i])
{
d[v[i]]=d[U]+1;
q.push(v[i]);
}
}
return d[T]!=-1;
}
ll dfs(int U,ll a)
{
if(U==T || !a) return a;
ll Flow=0,f;
for(int &i=cur[U];i!=-1;i=next[i])
if(d[U]+1==d[v[i]] && (f=dfs(v[i],min(a,cap[i]))))
{
cap[i]-=f; cap[i^1]+=f;
Flow+=f; a-=f; if(!a) break;
}
if(!Flow) d[U]=-1;
return Flow;
}
ll max_flow()
{
ll Flow=0,tmp=0;
while(bfs())
{
memcpy(cur,first,sizeof(first));
while(tmp=dfs(S,INF)) Flow+=tmp;
}
return Flow;
}
int n,m,pen,A,B,id[55][55];
char a[55][55];
int main(){
scanf("%d%d%d%d",&n,&m,&A,&B);
for(int i=1;i<=n;++i){
for(int j=1;j<=m;++j){
id[i][j]=++pen;
}
}
for(int i=1;i<=n;++i){
scanf("%s",a[i]+1);
}
S=pen+1;
T=S+1;
Init_Dinic();
for(int i=1;i<=n;++i){
for(int j=1;j<=m;++j){
if(a[i][j]=='.'){
AddEdge(S,id[i][j],(ll)B);
}
else{
AddEdge(id[i][j],T,(ll)B);
}
}
}
for(int i=1;i<=n;++i){
for(int j=1;j<=m;++j){
for(int k=0;k<4;++k){
int tx=i+dx[k],ty=j+dy[k];
if(tx>=1 && tx<=n && ty>=1 && ty<=m){
AddEdge(id[i][j],id[tx][ty],(ll)A);
}
}
}
}
printf("%lld\n",max_flow());
return 0;
}