Submission #1687036

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Source Code Expand

#include<iostream>
#include<vector>
#include<string>
#include<algorithm>	
#include<map>
#include<set>
#include<utility>
#include<cmath>
#include<cstring>
#include<queue>
#include<stack>
#include<cstdio>
#include<sstream>
#include<iomanip>
#include<assert.h>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define all(in) in.begin(),in.end()
#define shosu(x) fixed<<setprecision(x)
using namespace std;
//kaewasuretyuui
typedef long long ll;
typedef int Def;
typedef pair<Def,Def> pii;
typedef vector<Def> vi;
typedef vector<vi> vvi;
typedef vector<pii> vp;
typedef vector<vp> vvp;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef pair<Def,pii> pip;
typedef vector<pip>vip;
#define mt make_tuple
typedef tuple<pii,int,int> tp;
typedef vector<tp> vt;
template<typename A,typename B>bool cmin(A &a,const B &b){return a>b?(a=b,true):false;}
template<typename A,typename B>bool cmax(A &a,const B &b){return a<b?(a=b,true):false;}
const double PI=acos(-1);
const double EPS=1e-7;
Def inf=sizeof(Def)==sizeof(long long)?9e18:1e9;
int dx[]={0,1,0,-1,1,1,-1,-1};
int dy[]={1,0,-1,0,1,-1,1,-1};
int n;
vi in;
vvi G;
vi cyc;
pii dfs(int a){
	vi t;
	t.pb(inf);
	rep(i,G[a].size()){
		int to=G[a][i];
		if(cyc[to])continue;
		t.pb(dfs(to).first);
	}
	sort(all(t));
	pii out;
	int j;
	rep(i,t.size())if(t[i]!=i){
		out.first=i;
		t.pb(i);
		j=i;
		break;
	}
	sort(all(t));
	loop(i,j,t.size())if(t[i]!=i){
		out.second=i;
		t.pb(i);
		break;
	}
	return out;
}
int main(){
	cin>>n;
	in=vi(n);
	rep(i,n)cin>>in[i];
	rep(i,n)in[i]--;
	G=vvi(n);
	rep(i,n)G[in[i]].pb(i);
	cyc=vi(n);
	int t=0;
	while(cyc[t]==0){
		cyc[t]=true;
		t=in[t];
	}
	cyc=vi(n);
	while(cyc[t]==0){
		cyc[t]=true;
		t=in[t];
	}
//	rep(i,n)cout<<" "<<cyc[i];cout<<endl;
	vp num(n,{-1,-1});
	rep(i,n)if(cyc[i]){
		num[i]=dfs(i);
	}
//	rep(i,n)cout<<" "<<num[i].first<<" "<<num[i].second<<endl;
	rep(i,n)if(cyc[i]){
		int t=i;
		int nu=num[i].first;
		while(in[t]!=i){
			t=in[t];
			if(num[t].first==nu)nu=num[t].second;
			else nu=num[t].first;
		}
		if(num[i].first!=nu){
			cout<<"POSSIBLE"<<endl;
			return 0;
		}
		t=i;nu=num[i].second;
		while(in[t]!=i){
			t=in[t];
			if(num[t].first==nu)nu=num[t].second;
			else nu=num[t].first;
		}
		if(num[i].first==nu){
			cout<<"POSSIBLE"<<endl;
			return 0;
		}
		cout<<"IMPOSSIBLE"<<endl;
		return 0;
	}
}

Submission Info

Judge Result