HDU2767 Proving Equivalences

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<algorithm>
 4 #include<vector>
 5 #include<cstring>
 6 using namespace std;
 7 const int mxn=48000;
 8 int top,stack[mxn];
 9 bool inst[mxn];
10 int cnt,dnow;
11 int dfn[mxn],low[mxn];
12 int belone[mxn],in[mxn],out[mxn];
13 vector<int> e[mxn];
14 void clear(){
15     cnt=0;dnow=0;top=0;
16     memset(dfn,-1,sizeof(dfn));
17     memset(inst,false,sizeof(inst));
18     memset(in,0,sizeof in);
19     memset(out,0,sizeof out);
20     for(int i=1;i<mxn;i++) e[i].clear();
21 }
22 int n,m;
23 void tarjan(int s){
24     int v=0,i;
25     dfn[s]=++dnow;
26     low[s]=dfn[s];
27     inst[s]=true; 
28     stack[++top]=s;
29     int si=e[s].size();
30     for(i=0;i<si;i++){
31         v=e[s][i];
32         if(dfn[v]==-1){
33             tarjan(v);
34             low[s]=min(low[v],low[s]);
35         }
36         else if(inst[v]){
37             low[s]=min(dfn[v],low[s]);
38         }
39     }
40     if(dfn[s]==low[s]){
41         cnt++;
42         do{
43             v=stack[top--];
44             belone[v]=cnt;
45             inst[v]=false;
46         }while(s!=v);
47     }
48     return;
49 }
50 void calc(){
51     if(cnt==1){
52         printf("0\n");return;
53     }
54     int i,j;
55     for(i=1;i<=n;i++){
56         for(j=0;j<e[i].size();j++){
57             int v=e[i][j];
58             if(belone[i]!=belone[v]){
59                 in[belone[v]]++;
60                 out[belone[i]]++;
61             }
62         }
63     }
64     int idg=0,odg=0;
65     for(i=1;i<=cnt;i++){
66         if(!in[i])idg++;
67         if(!out[i])odg++;
68     }
69     printf("%d\n",max(idg,odg));
70     return;
71 }
72 int main(){
73     int T;
74     scanf("%d",&T);
75     while(T--){
76         scanf("%d%d",&n,&m);
77         if(!m){
78             if(n==1)printf("0\n");
79             else printf("%d\n",n);
80             continue;
81         }
82         clear();
83         int i,j;
84         int u,v;
85         for(i=1;i<=m;i++){
86             scanf("%d%d",&u,&v);
87             e[u].push_back(v);
88         }
89         for(i=1;i<=n;i++){
90             if(dfn[i]==-1)tarjan(i);
91         }
92         calc();
93     }
94     return 0;
95 }