bzoj1934: [Shoi2007]Vote 善意的投票

//Dinic是O(n2m)的。 
#include<cstdio>
#include<cstring>
#include<cctype>
#include<algorithm>
using namespace std;
#define rep(i,s,t) for(int i=s;i<=t;i++)
#define dwn(i,s,t) for(int i=s;i>=t;i--)
#define clr(x,c) memset(x,c,sizeof(x))
int read(){
    int x=0;char c=getchar();
    while(!isdigit(c)) c=getchar();
    while(isdigit(c)) x=x*10+c-‘0‘,c=getchar();
    return x;
}
const int nmax=305;
const int maxn=200000;
const int inf=0x7f7f7f7f;
struct edge{
    int to,cap;edge *next,*rev;
};
edge es[maxn],*pt=es,*head[nmax];
void add(int u,int v,int d){
    pt->to=v;pt->cap=d;pt->next=head[u];head[u]=pt++;
    pt->to=u;pt->cap=0;pt->next=head[v];head[v]=pt++;
    head[u]->rev=head[v];head[v]->rev=head[u];
}
edge *cur[nmax],*p[nmax];
int cnt[nmax],h[nmax];
int maxflow(int s,int t,int n){
    clr(cnt,0);cnt[0]=n;clr(h,0);
    int flow=0,a=inf,x=s;edge *e;
    while(h[s]<n){
        for(e=cur[x];e;e=e->next) if(e->cap>0&&h[x]==h[e->to]+1) break;
        if(e){
            a=min(a,e->cap);p[e->to]=cur[x]=e;x=e->to;
            if(x==t){
                while(x!=s) p[x]->cap-=a,p[x]->rev->cap+=a,x=p[x]->rev->to;
                flow+=a;a=inf;
            }
        }else{
            if(!--cnt[h[x]]) break;
            h[x]=n;
            for(e=head[x];e;e=e->next) if(e->cap>0&&h[x]>h[e->to]+1) h[x]=h[e->to]+1,cur[x]=e;
            cnt[h[x]]++;
            if(x!=s) x=p[x]->rev->to;
        }
    }
    return flow;
}
int main(){
    int n=read(),m=read(),u,v,s=0,t=n+1;
    rep(i,1,n) {
        u=read();
        (!u)?add(i,t,1):add(s,i,1);
    }
    rep(i,1,m) u=read(),v=read(),add(u,v,1),add(v,u,1);
    printf("%d\n",maxflow(s,t,t+1));
    return 0;
}