1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
| #include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
using namespace std;
#define REP(i,e,s) for(register int i=e; i<=s; i++)
#define DREP(i,e,s) for(register int i=e; i>=s; i--)
#define ll long long
#define DE(...) fprintf(stderr,__VA_ARGS__)
#define DEBUG(a) DE("DEBUG: %d\n",a)
#define file(a) freopen(a".in","r",stdin);freopen(a".out","w",stdout)
int read() {
int x=0,f=1,ch=getchar();
while(ch>'9'||ch<'0'){if(ch=='-')f=-1;ch=getchar();}
while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
return x*f;
}
const int MAXN=200000+10,MOD=1e9+7;
int fa[MAXN],size[MAXN],selfloop[MAXN],loop[MAXN];
int find(int x) {
if(fa[x]==x) return fa[x];
return fa[x]=find(fa[x]);
}
int link(int x,int y) {
fa[find(x)]=find(y);
}
int main() {
int n=read();
REP(i,1,(n<<1)) fa[i]=i,size[i]=1;
ll ans=1;
REP(i,1,n) {
int u=read(),v=read();
if(u==v) {selfloop[u]=1;continue;}
u=find(u),v=find(v);
if(u!=v) fa[u]=v,selfloop[v]|=selfloop[u],size[v]+=size[u];
else loop[u]=1;
}
REP(i,1,(n<<1))
if(find(i)==i&&!selfloop[i]) {
if(loop[i]) ans=1ll*ans*2;
else ans=1ll*ans*size[i];
ans%=MOD;
}
printf("%lld\n",ans);
return 0;
}
|
