【最小割】【Dinic】【强联通分量缩点】bzoj1797 [Ahoi2009]Mincut 最小割

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<vector>
 4 #include<algorithm>
 5 #include<queue>
 6 using namespace std;
 7 #define INF 2147483647
 8 #define MAXN 4011
 9 #define MAXM 120101
10 int v[MAXM],cap[MAXM],en,first[MAXN],next[MAXM];
11 int d[MAXN],cur[MAXN],cmp[MAXN],sum;
12 bool vis[MAXN];
13 queue<int>q;
14 vector<int>vs;
15 int n,m,S,T,A,B,C;
16 void Init_Dinic(){memset(first,-1,sizeof(first)); en=0;}
17 void AddEdge(const int &U,const int &V,const int &W)
18 {v[en]=V; cap[en]=W; next[en]=first[U]; first[U]=en++;
19 v[en]=U; next[en]=first[V]; first[V]=en++;}
20 bool bfs()
21 {
22     memset(d,-1,sizeof(d)); q.push(S); d[S]=0;
23     while(!q.empty())
24       {
25         int U=q.front(); q.pop();
26         for(int i=first[U];i!=-1;i=next[i])
27           if(d[v[i]]==-1 && cap[i])
28             {
29               d[v[i]]=d[U]+1;
30               q.push(v[i]);
31             }
32       }
33     return d[T]!=-1;
34 }
35 int dfs(int U,int a)
36 {
37     if(U==T || !a) return a;
38     int Flow=0,f;
39     for(int &i=cur[U];i!=-1;i=next[i])
40       if(d[U]+1==d[v[i]] && (f=dfs(v[i],min(a,cap[i]))))
41         {
42           cap[i]-=f; cap[i^1]+=f;
43           Flow+=f; a-=f; if(!a) break;
44         }
45     if(!Flow) d[U]=-1;
46     return Flow;
47 }
48 void max_flow()
49 {
50     while(bfs())
51       {
52         memcpy(cur,first,(n+5)*sizeof(int));
53         while(dfs(S,INF));
54       }
55 }
56 void dfs(int U)
57 {
58     vis[U]=1;
59     for(int i=first[U];i!=-1;i=next[i]) if(cap[i]&&(!vis[v[i]])) dfs(v[i]);
60     vs.push_back(U);
61 }
62 void dfs2(int U)
63 {
64     cmp[U]=sum;
65     for(int i=first[U];i!=-1;i=next[i]) if(cap[i^1]&&(!cmp[v[i]])) dfs2(v[i]);
66 }
67 void scc()
68 {
69     for(int i=1;i<=n;i++) if(!vis[i]) dfs(i);
70     vector<int>::iterator it=vs.end(); --it;
71     for(;;--it)
72       {
73         if(!cmp[*it]) {++sum; dfs2(*it);}
74         if(it==vs.begin()) break;
75       }
76 }
77 int main()
78 {
79     scanf("%d%d%d%d",&n,&m,&S,&T); Init_Dinic();
80     for(;m;--m)
81       {
82           scanf("%d%d%d",&A,&B,&C);
83           AddEdge(A,B,C);
84       }
85     max_flow(); scc();
86     for(int i=0;i<en;i+=2)
87       printf("%d %d\n",(!cap[i])&&cmp[v[i+1]]!=cmp[v[i]],(!cap[i])&&cmp[v[i+1]]==cmp[S]&&cmp[v[i]]==cmp[T]);
88     return 0;
89 }