bzoj1797: [Ahoi2009]Mincut 最小割（网络流，缩点）

 1 //minamoto
 2 #include<iostream>
 3 #include<cstdio>
 4 #include<cstring>
 5 #include<queue>
 6 #define inf 0x3f3f3f3f
 7 using namespace std;
 8 #define getc() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)
 9 char buf[1<<21],*p1=buf,*p2=buf;
10 template<class T>inline bool cmin(T&a,const T&b){return a>b?a=b,1:0;}
11 inline int read(){
12     #define num ch-‘0‘
13     char ch;bool flag=0;int res;
14     while(!isdigit(ch=getc()))
15     (ch==‘-‘)&&(flag=true);
16     for(res=num;isdigit(ch=getc());res=res*10+num);
17     (flag)&&(res=-res);
18     #undef num
19     return res;
20 }
21 const int N=4005,M=150005;
22 int head[N],Next[M],ver[M],edge[M],tot=1;
23 inline void add(int u,int v,int e){
24     ver[++tot]=v,Next[tot]=head[u],head[u]=tot,edge[tot]=e;
25     ver[++tot]=u,Next[tot]=head[v],head[v]=tot,edge[tot]=0;
26 }
27 int dep[N],cur[N],s,t,n,m;
28 queue<int> q;
29 bool bfs(){
30     memset(dep,-1,sizeof(dep));
31     while(!q.empty()) q.pop();
32     for(int i=1;i<=n;++i) cur[i]=head[i];
33     q.push(s),dep[s]=0;
34     while(!q.empty()){
35         int u=q.front();q.pop();
36         for(int i=head[u];i;i=Next[i]){
37             int v=ver[i];
38             if(dep[v]<0&&edge[i]){
39                 dep[v]=dep[u]+1,q.push(v);
40                 if(v==t) return true;
41             }
42         }
43     }
44     return false;
45 }
46 int dfs(int u,int limit){
47     if(u==t||!limit) return limit;
48     int flow=0,f;
49     for(int i=cur[u];i;i=Next[i]){
50         int v=ver[i];cur[u]=i;
51         if(dep[v]==dep[u]+1&&(f=dfs(v,min(limit,edge[i])))){
52             flow+=f,limit-=f;
53             edge[i]-=f,edge[i^1]+=f;
54             if(!limit) break;
55         }
56     }
57     if(!flow) dep[u]=-1;
58     return flow;
59 }
60 int dfn[N],low[N],st[N],c[N],top,cnt,num;
61 void tarjan(int u){
62     dfn[u]=low[u]=++num,st[++top]=u;
63     for(int i=head[u];i;i=Next[i])
64     if(edge[i]){
65         int v=ver[i];
66         if(!dfn[v]) tarjan(v),cmin(low[u],low[v]);
67         else if(!c[v]) cmin(low[u],dfn[v]);
68     }
69     if(dfn[u]==low[u])
70     for(++cnt;st[top+1]!=u;--top) c[st[top]]=cnt;
71 }
72 int main(){
73     //freopen("testdata.in","r",stdin);
74     n=read(),m=read(),s=read(),t=read();
75     for(int i=1;i<=m;++i){
76         int u=read(),v=read(),e=read();add(u,v,e);
77     }
78     while(bfs()) dfs(s,inf);
79     for(int i=1;i<=n;++i)
80     if(!dfn[i]) tarjan(i);
81     for(int i=2;i<=tot;i+=2){
82         printf("%d %d\n",!edge[i]&&c[ver[i]]!=c[ver[i^1]],c[ver[i^1]]==c[s]&&c[ver[i]]==c[t]);
83     }
84     return 0;
85 }