P2472 [SCOI2007]蜥蜴（网络流）

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
#define N 200005
inline int Min(int a,int b){return a<b?a:b;}
inline int Abs(int a){return a<0?-a:a;}
const int inf=1e8;
char a[25][25];
int R,C,D,S,T,d[N],cur[N],tot; bool vis[N];
int cnt=1,hd[N],nxt[N],ed[N],poi[N],val[N];
queue <int> h;
inline void adde(int x,int y,int v){
    nxt[ed[x]]=++cnt, hd[x]=hd[x]?hd[x]:cnt,
    ed[x]=cnt, poi[cnt]=y, val[cnt]=v;
}
inline void link(int x,int y,int v){adde(x,y,v),adde(y,x,0);}
inline int id(int x,int y){return (x-1)*C+y;}
bool Bfs(){
    memset(vis,0,sizeof(vis));
    h.push(S); vis[S]=1;
    while(!h.empty()){
        int x=h.front(); h.pop();
        for(int i=hd[x];i;i=nxt[i]){
            int to=poi[i];
            if(!vis[to]&&val[i]>0)
                vis[to]=1,d[to]=d[x]+1,h.push(to);
        }
    }return vis[T];
}
int Dfs(int x,int a){
    if(x==T||a==0) return a; 
    int F=0,f;
    for(int &i=cur[x];i&&a;i=nxt[i]){
        int to=poi[i];
        if(d[to]==d[x]+1&&(f=(Dfs(to,Min(a,val[i]))))>0)
            F+=f,a-=f,val[i]-=f,val[i^1]+=f;
    }return F;
}
int dinic(){
    int re=0;
    while(Bfs()){
        for(int i=1;i<=T;++i) cur[i]=hd[i];
        re+=Dfs(S,inf);
    }return re;
}
void draw(int x,int y){//向周围距离<=d的点连边
    if(a[x][y]==‘0‘) return ;
    int p=id(x,y); bool tt=1;
    link(p<<1,p<<1|1,a[x][y]-‘0‘);
    for(int i=x-D;i<=x+D;++i)
        for(int j=y-D;j<=y+D;++j){
            if((i==x&&j==y)||Abs(x-i)+Abs(y-j)>D) continue;
            if(i>0&&i<=R&&j>0&&j<=C) link(p<<1|1,id(i,j)<<1,inf);
            else if(tt) link(p<<1|1,T,inf),tt=0;
        }
}
int main(){
    scanf("%d%d%d",&R,&C,&D);
    S=R*C*2+2; T=S+1;
    for(int i=1;i<=R;++i) scanf("%s",a[i]+1);
    for(int i=1;i<=R;++i)
        for(int j=1;j<=C;++j)
            draw(i,j);
    for(int i=1;i<=R;++i) scanf("%s",a[i]+1);
    for(int i=1;i<=R;++i)
        for(int j=1;j<=C;++j)
            if(a[i][j]==‘L‘)
                link(S,id(i,j)<<1,1),++tot;
    printf("%d",tot-dinic());
    return 0;
}