BZOJ 1443 二分图博弈 网络流

思路：

二分图博弈嘛 找到最大匹配的必须点

跑个网络流 前后DFS一遍  

//By SiriusRen
#include <queue>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int N=105,M=105*105*35,inf=0x3f3f3f3f;
int n,m,id[N][N],cnt,T,vis[M/8],jy;
char ch[115][115],xx[]={1,-1,0,0},yy[]={0,0,1,-1};
struct Dinic{
    int first[M],next[M],v[M],w[M],tot,top,ans[M],color[M],recx[M],recy[M];
    void init(){memset(first,-1,sizeof(first));}
    void Add(int x,int y,int z){w[tot]=z,v[tot]=y,next[tot]=first[x],first[x]=tot++;}
    void add(int x,int y,int z){Add(x,y,z),Add(y,x,0);}
    void build(){
        init(),T=cnt+1,color[T]=1;
        for(int i=1;i<=n;i++)
            for(int j=1;j<=m;j++)if(id[i][j]){
                recx[id[i][j]]=i,recy[id[i][j]]=j;
                if((i+j)&1){
                    add(0,id[i][j],1),color[id[i][j]]=1;
                    for(int k=0;k<4;k++){
                        int dx=i+xx[k],dy=j+yy[k];
                        if(id[dx][dy])add(id[i][j],id[dx][dy],1);
                    }
                }
                else add(id[i][j],T,1);
            }
        flow();
        if(!cnt)puts("LOSE");
        else{
            puts("WIN");
            memset(vis,0,sizeof(vis)),dfs(0,1);
            memset(vis,0,sizeof(vis)),dfs(T,0);
            sort(ans+1,ans+1+top);
            for(int i=1;i<=top;i++)printf("%d %d\n",recx[ans[i]],recy[ans[i]]);
        }
    }
    bool tell(){
        memset(vis,-1,sizeof(vis));
        queue<int>q;q.push(0),vis[0]=0;
        while(!q.empty()){
            int t=q.front();q.pop();
            for(int i=first[t];~i;i=next[i])
                if(vis[v[i]]==-1&&w[i])vis[v[i]]=vis[t]+1,q.push(v[i]);
        }return ~vis[T];
    }
    int zeng(int x,int y){
        if(x==T)return y;
        int r=0;
        for(int i=first[x];~i;i=next[i])if(vis[v[i]]==vis[x]+1&&w[i]){
            int t=zeng(v[i],min(w[i],y-r));
            w[i]-=t,w[i^1]+=t,r+=t;
        }if(!r)vis[x]=-1;
        return r;
    }
    int flow(){while(tell())while(jy=zeng(0,inf))cnt-=jy*2;}
    void dfs(int x,int y){
        if(color[x]==y)ans[++top]=x;
        for(int i=first[x];~i;i=next[i])if(w[i]==y&&!vis[v[i]])vis[v[i]]=1,dfs(v[i],y);
    }
}dinic;
int main(){
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++)scanf("%s",ch[i]+1);
    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)
            if(ch[i][j]=='.')id[i][j]=++cnt;
    dinic.build();
}