Longest route

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

constexpr int NMX = (int)1e5;
vector<int> adj[NMX];
map<int,int> par;
vector<int> dist(NMX);

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);
	}
	priority_queue<tuple<int,int,int>> q;
	q.push({1, 0, 1});
	while (!q.empty()) {
		auto [adist, a, b] = q.top(); q.pop();
		if (adist <= dist[b]) continue;
		dist[b] = adist;
		par[b] = a;
		for (int nb : adj[b]) {
			q.push({(dist[b]+1), b, nb});
		}
	}
	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);
	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: WRONG ANSWER

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: WRONG ANSWER

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: WRONG ANSWER

Test 15

Verdict: TIME LIMIT EXCEEDED

Test 16

Verdict: WRONG ANSWER

Test 17

Verdict: WRONG ANSWER

Test 18

Verdict: TIME LIMIT EXCEEDED

Test 19

Verdict: WRONG ANSWER

Test 20

Verdict: WRONG ANSWER

Test 21

Verdict: WRONG ANSWER