Longest route

input/code.cpp: In function 'int main()':
input/code.cpp:63:15: warning: comparison of integer expressions of different signedness: 'long long unsigned int' and 'int' [-Wsign-compare]
   63 |   while (curr != -1) {
      |          ~~~~~^~~~~
input/code.cpp:53:8: warning: unused variable 'success' [-Wunused-variable]
   53 |   char success = 0;
      |        ^~~~~~~

#include <bits/stdc++.h>
#define ll unsigned long long

template <typename T>
std::ostream &operator<<(std::ostream &os, const std::vector<T> &v) {
  os << "[";
  for (int i = 0; i < v.size(); ++i) {
    os << v[i];
    if (i != v.size() - 1)
      os << ", ";
  }
  os << "]";
  return os;
}

std::pair<ll, ll> dfs(std::vector<std::vector<ll>> &connMap,
                      std::vector<ll> &parentMap, ll curr, ll end) {
  if (curr == end) {
    return std::pair<ll, ll>({0, 1});
  }

  ll maRet = 0;
  ll succ = 0;
  for (ll next : connMap[curr]) {
    std::pair<ll, ll> ret = dfs(connMap, parentMap, next, end);
    if (ret.first >= maRet && ret.second) {
      succ = ret.second;
      //   std::cout << "Pöö " << curr << std::endl;
      parentMap[next] = curr;
      maRet = ret.first;
    }
  }
  return std::pair<ll, ll>({maRet + 1, succ});
}

int main() {
  ll cityCount, flightCount;
  std::cin >> cityCount;
  std::cin >> flightCount;
  // std::vector<ll> heights(cityCount, -1);

  std::vector<std::vector<ll>> connMap(cityCount);
  for (ll ii = 0; ii < flightCount; ii++) {
    ll start, end;
    std::cin >> start;
    std::cin >> end;
    connMap[start - 1].push_back(end - 1);
    // connMap[end - 1].push_back({start - 1});
  }
  //   std::cout << connMap << std::endl;

  std::vector<ll> parentMap(cityCount, -1);
  char success = 0;
  std::pair<ll, ll> dfsRet = dfs(connMap, parentMap, 0, cityCount - 1);
  if (!dfsRet.second) {
    std::cout << "IMPOSSIBLE" << std::endl;
    return 0;
  }
  ll curr = cityCount - 1;
  //   std::cout << "dfsRet " << dfsRet.first << std::endl;
  std::vector<ll> retThing;
  //   std::cout << parentMap << std::endl;
  while (curr != -1) {
    // std::cout << curr + 1 << " ";
    retThing.push_back(curr + 1);
    curr = parentMap[curr];
  }
  std::cout << retThing.size() << std::endl;
  for (int ii = retThing.size() - 1; ii > 0; ii--) {
    std::cout << retThing[ii] << " ";
  }
  std::cout << retThing[0] << std::endl;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

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: ACCEPTED

Test 12

Verdict: TIME LIMIT EXCEEDED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: TIME LIMIT EXCEEDED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: TIME LIMIT EXCEEDED

Test 18

Verdict: TIME LIMIT EXCEEDED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED