Graph Ordering

input/code.cpp: In function 'int main()':
input/code.cpp:124:9: warning: ignoring return value of 'int system(const char*)', declared with attribute warn_unused_result [-Wunused-result]
   system("pause");
   ~~~~~~^~~~~~~~~
input/code.cpp:144:8: warning: ignoring return value of 'int system(const char*)', declared with attribute warn_unused_result [-Wunused-result]
  system("pause");
  ~~~~~~^~~~~~~~~

#define _CRT_SECURE_NO_DEPRECATE
#include <algorithm>
#include <numeric>
#include <iterator>
#include <string>
#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
#include <map>
#include <queue>
using namespace std;
typedef long long		ll;
typedef pair<int, int>	ii;
typedef vector<ii>		vii;
typedef vector<int>		vi;
#define INF 1000000000
#define REP(i, a, b) for (int i = int(a); i < int(b); ++i)




vi ans;

void visit(int p, const vector<vi> & nabo, vector<vector<bool> > & nabo_valid,
	vector<char> & mark, queue<int> & temp_nodes, vi & naboer) {

	if (mark[p] == 'P')
		return;

	mark[p] = 'P';
	ans.push_back(p);

	REP(i, 0, nabo[p].size()) {
		int q = nabo[p][i];

		//naboen er ikke besøkt
		if (mark[q] != 'T' && mark[q] != 'P') {
			//trekk kant fra p til q
			naboer[q]--;
			//utvid fra nodene i nød
			if (naboer[q] == 1)
				visit(q, nabo, nabo_valid, mark, temp_nodes, naboer);
			//ellers spar dem og se hva gjøre
			else
				temp_nodes.push(q);
		}
	}
	/*mark[p] = 'P';

	ans.push_back(p);*/


	//if (mark[p] == 'P')
	//	return;

	//mark[p] = 'T';
	//REP(i, 0, nabo[p].size()) {
	//	//naboen
	//	int q = nabo[p][i];

	//	//denne veien settes som ugyldig
	//	if (mark[q] == 'T')
	//		nabo_valid[p][i] = false;
	//	else
	//		visit(q, nabo, nabo_valid, mark);
	//}
	//mark[p] = 'P';
	//ans.push_back(p);
}


int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);

	//nodes and edges
	int n, m;
	cin >> n >> m;

	//naboliste
	vector<vi> nabo(n + 1);
	//gyldig å gå denne veien?
	vector<vector<bool> > nabo_valid(n + 1);


	REP(i, 0, m) {
		int p, q;
		cin >> p >> q;
		//anta går begge veier
		nabo[p].push_back(q);
		nabo_valid[p].push_back(true);

		nabo[q].push_back(p);
		nabo_valid[q].push_back(true);
	}

	//antall kandidater for source
	int n_cand = 0;
	vi cand;
	vi naboer(n + 1);
	//teller antall naboer til hver node
	REP(i, 1, n + 1) {
		naboer[i] = nabo[i].size();
		if (naboer[i] == 1) {
			n_cand++;
			cand.push_back(i);
		}
	}

	if (n_cand == 2) {
		//la siste kandidat være sink
		cand.pop_back();
	}

	if (n_cand == 0) {
		//velg vilkårlig node som source
		cand.push_back(1);
	}

	//umulig
	if (n_cand > 2) {
		cout << "IMPOSSIBLE" << endl;
		system("pause");
		return 0;
	}

	vector<char> mark(n + 1, 'N');
	queue<int> temp_nodes;
	temp_nodes.push(cand[0]);
	
	while (!temp_nodes.empty()) {
		int t = temp_nodes.front();
		temp_nodes.pop();

		visit(t, nabo, nabo_valid, mark, temp_nodes, naboer);
	}
	

	for (int z : ans)
		cout << z << " ";
	cout << endl;
	
	system("pause");
	return 0;
}

Test 1

Group: 1, 4, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 2

Group: 1, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 3

Group: 1, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 4

Group: 1, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 5

Group: 1, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 6

Group: 2, 3, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 7

Group: 2, 3, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 8

Group: 2, 3, 4, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 9

Group: 2, 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 10

Group: 2, 3, 4, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 11

Group: 2, 3, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 12

Group: 2, 3, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 13

Group: 2, 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 14

Group: 2, 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 15

Group: 2, 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 16

Group: 2, 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 17

Group: 2, 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 18

Group: 2, 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 19

Group: 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 20

Group: 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 21

Group: 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 22

Group: 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 23

Group: 3, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 24

Group: 3, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 25

Group: 3, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 26

Group: 3, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 27

Group: 3, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 28

Group: 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 29

Group: 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 30

Group: 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 31

Group: 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 32

Group: 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 33

Group: 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 34

Group: 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 35

Group: 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 36

Group: 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 37

Group: 1, 2, 3, 4, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 38

Group: 2, 3, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 39

Group: 2, 3, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 40

Group: 2, 3, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 41

Group: 1, 2, 3, 5

Verdict: ACCEPTED

sh: 1: pause: not found

Test 42

Group: 2, 3, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 43

Group: 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 44

Group: 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 45

Group: 2, 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 46

Group: 2, 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 47

Group: 2, 3, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 48

Group: 3, 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found

Test 49

Group: 4, 5

Verdict: WRONG ANSWER

sh: 1: pause: not found