Submission #1481478

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Source Code Expand

// This amazing code is by Eric Sunli Chen.
#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <utility>
#include <vector>
using namespace std;
template<typename T> void get_int(T &x)
{
	char t=getchar();
	bool neg=false;
	x=0;
	for(; (t>'9'||t<'0')&&t!='-'; t=getchar());
	if(t=='-')neg=true,t=getchar();
	for(; t<='9'&&t>='0'; t=getchar())x=x*10+t-'0';
	if(neg)x=-x;
}
template<typename T> void print_int(T x)
{
	if(x<0)putchar('-'),x=-x;
	short a[20]= {},sz=0;
	while(x>0)a[sz++]=x%10,x/=10;
	if(sz==0)putchar('0');
	for(int i=sz-1; i>=0; i--)putchar('0'+a[i]);
}
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define get1(a) get_int(a)
#define get2(a,b) get1(a),get1(b)
#define get3(a,b,c) get1(a),get2(b,c)
#define printendl(a) print_int(a),puts("")
typedef long long LL;
typedef unsigned long long uLL;
typedef pair<int,int> pii;
const int inf=0x3f3f3f3f;
const LL Linf=1ll<<61;
const double pi=acos(-1.0);

const int mod=1e9+7;

vector<int> g[100111],id[100111],v,cyc;
int n,a[100111],fa[100111],dep[100111];
bool use[100111];

void dfs(int x,int f=0,int fid=0)
{
	fa[x]=f;
	use[x]=1;v.pb(x);
	for(int i=0;i<(int)g[x].size();i++)
		if(!use[g[x][i]])
		{
			dep[g[x][i]]=dep[x]+1;
			dfs(g[x][i],x,id[x][i]);
		}
		else if(id[x][i]!=fid&&dep[g[x][i]]<=dep[x])
		{
			int cur=x;
			while(cur!=g[x][i])
			{
				cyc.pb(cur);
				cur=fa[cur];
			}
			cyc.pb(cur);
			if(a[f]==x)reverse(cyc.begin(),cyc.end());
		}
}
bool in[100111];
int sz[100111],cur;
bool dfs2(int x,int f=0)
{
	cur++;
	int ch=0;
	for(int i=0;i<(int)g[x].size();i++)
		if(!in[g[x][i]]&&g[x][i]!=f)
		{
			ch++;
			if(!dfs2(g[x][i],x))return false;
		}
	if(ch>1)return false;
	return true;
}
int calc()
{
	for(int i=0;i<(int)cyc.size();i++)in[cyc[i]]=1;
	for(int i=0;i<(int)cyc.size();i++)
	{
		cur=-1;
		if(!dfs2(cyc[i]))return 0;
		sz[i]=cur;
	}
	int last=0;for(int i=0;i<(int)cyc.size();i++)if(sz[i])last=i;
	int ret=1;
	for(int i=0;i<(int)cyc.size();i++)
	{
		if(sz[i]==0)continue;
		int len=i-last;if(len<=0)len+=(int)cyc.size();
		if(len<sz[i])return 0;
		else if(len>sz[i])ret=(ret+ret)%mod;
		last=i;
	}
	return ret;
}

int frq[100111],ans,dp[100111];
int main()
{
	get1(n);
	for(int i=1;i<=n;i++)
	{
		get1(a[i]);
		g[i].pb(a[i]);id[i].pb(i);
		if(a[i]!=i)
		{
			g[a[i]].pb(i);
			id[a[i]].pb(i);
		}
	}
	ans=1;
	for(int i=1;i<=n;i++)
	{
		if(use[i])continue;
		v.clear();cyc.clear();
		dfs(i);
		if((int)v.size()==(int)cyc.size())
			frq[(int)v.size()]++;
		else ans=1ll*ans*calc()%mod;
	}
	for(int i=1;i<=n;i++)
	{
		dp[0]=1;
		for(int j=1;j<=frq[i];j++)
		{
			dp[j]=dp[j-1];
			if(i>1&&i%2)dp[j]=(dp[j]+dp[j-1])%mod;
			if(j>1)dp[j]=(dp[j]+1ll*dp[j-2]*(j-1)%mod*i)%mod;
		}
		ans=1ll*ans*dp[frq[i]]%mod;
	}
	printendl(ans);
	return 0;
}

Submission Info

Judge Result