BZOJ-1934: [Shoi2007]Vote 善意的投票 (网络流最小割)

 1 #include "bits/stdc++.h"
 2 using namespace std;
 3 typedef long long LL;
 4 const int MAX=305;
 5 const int M=MAX*MAX;
 6 int n,m,s,t;
 7 int tot,head[MAX],adj[M],wei[M],next[M];
 8 int deep[MAX],cur[MAX];
 9 inline int read(){
10     int an=0,x=1;char c=getchar();
11     while (c<‘0‘ || c>‘9‘) {if (c==‘-‘) x=-1;c=getchar();}
12     while (c>=‘0‘ && c<=‘9‘) {an=(an<<3)+(an<<1)+c-‘0‘;c=getchar();}
13     return an*x;
14 }
15 void addedge(int u,int v,int w){
16     tot++;adj[tot]=v,wei[tot]=w,next[tot]=head[u],head[u]=tot;
17 }
18 bool bfs(){
19     int i,j,u;
20     memset(deep,127,sizeof(deep));
21     deep[s]=0;
22     queue <int> q;q.push(s);
23     while (!q.empty()){
24         u=q.front();q.pop();
25         for (i=head[u];i;i=next[i]){
26             if (deep[adj[i]]>1e9 && wei[i]>0)
27                 deep[adj[i]]=deep[u]+1,q.push(adj[i]);
28         }
29     }
30     return deep[t]<1e9;
31 }
32 int dfs(int x,int flo){
33     if (x==t || flo==0) return flo;
34     int j;
35     for (int &i=cur[x];i;i=next[i]){
36         if (deep[adj[i]]==deep[x]+1 && wei[i]>0){
37             j=dfs(adj[i],min(flo,wei[i]));
38             if (j){
39                 wei[i]-=j,wei[i^1]+=j;
40                 return j;
41             }
42         }
43     }
44     return 0;
45 }
46 int main(){
47     freopen ("vote.in","r",stdin);freopen ("vote.out","w",stdout);
48     int i,j,u,v;
49     n=read(),m=read();tot=1;s=n+1,t=n+2;
50     for (i=1;i<=n;i++){
51         u=read();
52         if (u==1) addedge(s,i,1),addedge(i,s,0);
53         else addedge(i
54         ,t,1),addedge(t,i,0);
55     }
56     for (i=1;i<=m;i++){
57         u=read();v=read();
58         addedge(u,v,1),addedge(v,u,1);
59     }
60     int flow=0,dd;
61     while (bfs()){
62         for (i=1;i<=n+2;i++) cur[i]=head[i];
63         while (dd=dfs(s,1e9)) flow+=dd;
64     }
65     printf("%d",flow);
66     return 0;
67 }