【BZOJ 1934】 [Shoi2007]Vote 善意的投票

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<cmath>
 4 #include<iostream>
 5 using namespace std;
 6 const int inf=100000000,N=310;
 7 struct ee{int to,next,f;}e[N*N*2];
 8 int head[N],q[N*2],dis[N],x[N];
 9 int S,T,n,m,cnt=1,ans,w;
10   
11 void ins(int u,int v,int f){
12     e[++cnt].to=v;e[cnt].f=f;e[cnt].next=head[u];head[u]=cnt;
13     e[++cnt].to=u;e[cnt].f=0;e[cnt].next=head[v];head[v]=cnt;
14 }
15   
16 bool bfs(){
17     for (int i=1;i<=T;i++) dis[i]=inf;
18     int h=0,t=1,now;
19     q[1]=S;dis[S]=0;
20     while(h!=t){
21         now=q[++h];
22         for (int i=head[now];i;i=e[i].next){
23             int v=e[i].to;
24             if (e[i].f&&dis[now]+1<dis[v]){
25                 dis[v]=dis[now]+1;
26                 if (v==T)return 1;
27                 q[++t]=v;
28             }
29         }
30     }
31     if (dis[T]==inf) return 0; return 1;
32 }
33   
34 int dinic(int now,int f){
35     if (now==T) return f;
36     int rest=f;
37     for (int i=head[now];i;i=e[i].next){
38         int v=e[i].to;
39         if (e[i].f&&dis[v]==dis[now]+1&&rest){
40             int t=dinic(v,min(rest,e[i].f));
41             if (!t) dis[v]=0;
42             e[i].f-=t;
43             e[i^1].f+=t;
44             rest-=t;
45             //if(t) printf("%d %d %d\n",now,v,e[i].f);
46         }
47     }
48     return f-rest;
49 }
50 int main(){
51     scanf("%d%d",&n,&m);
52     S=0,T=n+1;
53     for (int i=1;i<=n;i++) {
54         scanf("%d",&x[i]);
55         if (x[i]==0) ins(S,i,1),ins(i,T,0);
56         else ins(S,i,0),ins(i,T,1);
57     }
58     int u,v;
59     for (int i=1;i<=m;i++){
60         scanf("%d%d",&u,&v);
61         ins(u,v,1);ins(v,u,1);
62     }
63     while (bfs()) ans+=dinic(S,inf);
64     printf("%d",ans);
65 }