bzoj1934[Shoi2007]Vote 善意的投票

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <queue>
 5 #define maxn 500
 6 #define inc(i,j,k) for(int i=j;i<=k;i++)
 7 #define INF 0x3fffffff
 8 using namespace std;
 9 
10 struct e{int t,c,n;}; e es[maxn*2000]; int g[maxn],ess;
11 inline void pe(int f,int t,int c){
12     es[++ess]=(e){t,c,g[f]}; g[f]=ess; es[++ess]=(e){f,0,g[t]}; g[t]=ess;
13 }
14 inline void pe2(int f,int t,int c){
15     es[++ess]=(e){t,c,g[f]}; g[f]=ess; es[++ess]=(e){f,c,g[t]}; g[t]=ess;
16 }
17 inline void init(){
18     ess=-1; memset(g,-1,sizeof(g));
19 }
20 queue <int> q; int h[maxn];
21 bool bfs(int s,int t){
22     memset(h,-1,sizeof(h)); while(!q.empty())q.pop(); h[s]=0; q.push(s);
23     while(! q.empty()){
24         int x=q.front(); q.pop();
25         for(int i=g[x];i!=-1;i=es[i].n)if(es[i].c&&h[es[i].t]==-1)h[es[i].t]=h[x]+1,q.push(es[i].t);
26     }
27     return h[t]!=-1;
28 }
29 int dfs(int x,int t,int f){
30     if(x==t)return f; int u=0;
31     for(int i=g[x];i!=-1;i=es[i].n)if(es[i].c&&h[es[i].t]==h[x]+1){
32         int w=dfs(es[i].t,t,min(f,es[i].c)); f-=w; u+=w; es[i].c-=w; es[i^1].c+=w; if(f==0)return u;
33     }
34     if(u==0)h[x]=-1; return u;
35 }
36 int dinic(int s,int t){
37     int f=0; while(bfs(s,t))f+=dfs(s,t,INF); return f;
38 }
39 inline int read(){
40     char ch=getchar(); int f=1,x=0;
41     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1; ch=getchar();} while(ch>=‘0‘&&ch<=‘9‘)x=x*10+ch-‘0‘,ch=getchar();
42     return x*f;
43 }
44 int n,m,s,t;
45 int main(){
46     n=read(); m=read(); s=0; t=n+1; init(); inc(i,1,n){int x=read(); if(x)pe(s,i,1);else pe(i,t,1);}
47     inc(i,1,m){int x=read(),y=read(); pe2(x,y,1);} printf("%d",dinic(s,t)); return 0;
48 }