#include "islands.h"
#include<bits/stdc++.h>
using namespace std;
#define rep(a, b) for(int a = 0; a < (b); ++a)
#define st first
#define nd second
#define pb push_back
#define all(a) a.begin(), a.end()
const int LIM=2e5+7;
vector<pair<int,int>>V[LIM];
vector<int>cykl;
int odw[LIM], czy[LIM];
int DFS(int x) {
odw[x]=1;
for(auto i : V[x]) if(odw[i.st]) {
czy[i.nd]=1;
cykl.pb(i.nd);
return i.st;
}
for(auto i : V[x]) {
if(!odw[i.st]) {
int p=DFS(i.st);
if(p==-1) continue;
if(p>=0) cykl.pb(i.nd);
if(p==x) p=-2;
return p;
}
}
return -1;
}
variant<bool,vector<int>>find_journey(int n, int m, vector<int>X, vector<int>Y) {
rep(i, m) V[X[i]].pb({Y[i], i});
if(DFS(0)==-1) return false;
rep(i, n) V[i].clear();
for(auto i : cykl) swap(X[i], Y[i]);
rep(i, m) if(!czy[i]) V[X[i]].pb({Y[i], i});
if(DFS(0)==-1) return false;
return true;
}
