Longest route

input/code.cpp: In function 'int main()':
input/code.cpp:39:24: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   39 |         for (int i=0; i<outl.size(); i++) {
      |                       ~^~~~~~~~~~~~
input/code.cpp:44:24: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   44 |         for (int i=1; i<=outr.size(); i++) {
      |                       ~^~~~~~~~~~~~~

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

constexpr int NMX = (int)1e5;
vector<int> adj[NMX];
vector<int> into[NMX];
vector<int> vis(NMX);
vector<int> outl;
vector<int> outr;
map<int,int> par;


int main() {
	int n, m;
	cin >> n >> m;
	for (int i=0; i<m; i++) {
		int a, b;
		cin >> a >> b;
		adj[a].push_back(b);
		into[b].push_back(a);
	}
	stack<int> q;
	q.push(1);
	while (!q.empty()) {
		int a = q.top(); q.pop();
		if (vis[a] == 2) continue;
		if (vis[a] == 1) {
			vis[a] = 2;
			outl.push_back(a);
			continue;
		}
		vis[a] = 1;
		q.push(a);
		for (int nb : adj[a]) {
			q.push(nb);
		}
	}
	for (int i=0; i<outl.size(); i++) {
		outr.push_back(outl[outl.size()-1-i]);
	}

	vector<int> mem(outl.size()+2);
	for (int i=1; i<=outr.size(); i++) {
		int maxn = 0;
		int maxb = 0;
		for (int nb : into[i]) {
			if (mem[nb] > maxn) {
				maxn = mem[nb];
				maxb = nb;
			}
		}
		par[i] = maxb;
		mem[i] = maxn+1;
	}

	int cur = n;
	vector<int> out;
	while (cur != 1) {
		out.push_back(cur);
		cur = par[cur];
		if (cur == 0) {
			cout << "IMPOSSIBLE";
			return 0;
		}
	}
	out.push_back(1);
	cout << out.size() << "\n";
	for (int i=out.size()-1; i>=0; i--) {
		cout << out[i] << " ";
	}
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: ACCEPTED

Test 5

Verdict: WRONG ANSWER

Test 6

Verdict: ACCEPTED

Test 7

Verdict: RUNTIME ERROR

Test 8

Verdict: RUNTIME ERROR

Test 9

Verdict: RUNTIME ERROR

Test 10

Verdict: RUNTIME ERROR

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: WRONG ANSWER

Test 18

Verdict: ACCEPTED

Test 19

Verdict: WRONG ANSWER

Test 20

Verdict: ACCEPTED

Test 21

Verdict: WRONG ANSWER