C++之路进阶——最大流（善意的投票）

 1 #include<cstdio>
 2 #include<queue>
 3 #include<cstring>
 4 #define maxn 310
 5 #include<iostream>
 6   
 7 using namespace std;
 8   
 9 int S=0,T,head[maxn],dis[maxn],maxlow,ans,cnt=1,n,m,x[maxn];
10 struct ss
11    {
12     int to;
13     int next;
14     int edge;
15    }e[130100];
16   
17 void add(int u,int v,int w)
18     {
19         e[++cnt].next=head[u];
20         head[u]=cnt;
21         e[cnt].to=v;
22         e[cnt].edge=w;
23     }
24   
25 void insert(int u,int v,int w)
26     {
27         add(u,v,w);
28         add(v,u,0);
29     } 
30      
31 bool bfs()
32     {
33         for (int i=1;i<=T;i++) dis[i]=0x7fffffff;
34         queue<int>que;
35         que.push(S);
36         dis[0]=0;
37         while (!que.empty())
38            {
39              int now=que.front();
40              que.pop();
41              for (int i=head[now];i;i=e[i].next)
42                if (e[i].edge&&dis[e[i].to]>dis[now]+1)
43                 {
44                    dis[e[i].to]=dis[now]+1;
45                    que.push(e[i].to);
46                    if (e[i].to==T)  return 1;    
47                 }
48            }
49       return 0;    
50     }     
51   
52 int dinic(int x,int inf)
53     {
54       if (x==T) return inf; 
55       int rest=inf;
56       for (int i=head[x];i&&rest;i=e[i].next)
57         if (e[i].edge&&dis[e[i].to]==dis[x]+1) 
58          {
59             int now=dinic(e[i].to,min(rest,e[i].edge));
60             if (!now) dis[now]=0;
61             e[i].edge-=now;
62             e[i^1].edge+=now;
63             rest-=now;
64          }  
65      return inf-rest;    
66     }
67   
68 int main()
69    {
70      scanf("%d%d",&n,&m);
71      T=n+1;
72      for (int i=1;i<=n;i++)
73        {
74           int x;
75           scanf("%d",&x);
76           if (x)
77                insert(0,i,1),insert(i,T,0);
78               else
79                insert(i,T,1),insert(0,i,0);     
80        }
81      for (int i=1;i<=m;i++)
82         {
83            int u,v;
84            scanf("%d%d",&u,&v);
85            insert(u,v,1);
86            insert(v,u,1);   
87         } 
88     while (bfs()) 
89        while (ans=dinic(S,0x7fffffff)) maxlow+=ans;
90     printf("%d\n",maxlow);   
91     return 0;
92    }