bzoj 1412: [ZJOI2009]狼和羊的故事

http://www.lydsy.com/JudgeOnline/problem.php?id=1412

超级源点连向所有的狼，超级汇点连向所有羊，流量为INF

相邻连边流量为1，最小割

#include<cstdio>
#include<queue>
#include<cstring>
#include<algorithm>
std::queue<int>que;
int fs[]={,,,-,};
#define INF 0x7fffffff
const int maxn = ;
int map[][];
inline int read() {
    int x=;
    char c=getchar();
    while(c<''||c>'')c=getchar();
    while(c<=''&&c>='')x=x*+c-'',c=getchar();
    return x;
}
int n,m,S,T,src,decc;
struct node{
    int v,next,flow;
}edge[maxn];int head[maxn],num=,cur[maxn],lev[maxn];
void add_edge(int u,int v,int w) {
    edge[++num].v=v;edge[num].next=head[u];head[u]=num;
    edge[num].flow=w;
}
bool bfs() {
    while(!que.empty()) que.pop();
    std::memset(lev,-,sizeof lev);
    memcpy(cur,head,sizeof head);
    lev[src]=;
    que.push(src);int now;
    while(!que.empty()) {
        now=que.front();que.pop();
        for(int i=head[now];i;i=edge[i].next) {
            int v=edge[i].v;
            if(lev[v]==-&&edge[i].flow>) {
                lev[v]=lev[now]+;
                if(v==decc)return true;
                que.push(v);
            }
        }
    }
    return false;
}
int dfs(int now,int flow) {
    if(now==decc)return flow;
    int rest=,delta;
    for(int &i=cur[now];i;i=edge[i].next) {
        int v=edge[i].v;
        if(lev[v]==lev[now]+&&edge[i].flow>) {
            delta=dfs(v,std::min(flow-rest,edge[i].flow));
            if(delta) {
                edge[i].flow-=delta;
                edge[i^].flow+=delta;
                rest+=delta;if(rest==flow)break;
            }
        }
    }
    if(rest==flow)lev[now]=-;//满流
    return rest;
}
int Dinic() {
    int ans=;
    while(bfs())
        ans+=dfs(src,INF);
    return ans;
}
inline void add(int a,int b,int flow) {
    add_edge(a,b,flow);add_edge(b,a,);
}
inline int calc(int i,int j) {
    return (i-)*m+j;
}
int main() {
    n=read(),m=read();
    src=;decc=n*m+;
    for(int i=;i<=n;++i)
        for(int j=;j<=m;++j)
            map[i][j]=read();
    for(int i=;i<=n;++i) {
        for(int j=;j<=m;++j) {
            if(map[i][j]==)add(src,calc(i,j),INF);
            else if(map[i][j]==){ add(calc(i,j),decc,INF);continue;}
            for(int k=;k<;++k) {
                int x=i+fs[k],y=j+fs[k+];
                if(x<=||x>n||y<=||y>m)continue;
                add(calc(i,j),calc(x,y),);
            }
        }
    }
    printf("%d\n",Dinic());
    return ;
}