Problem p03812 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

using VI = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;
using LL = long long;
using VL = vector<LL>;
using VVL = vector<VL>;
using PLL = pair<LL, LL>;
using VS = vector<string>;

#define ALL(a) begin((a)), end((a))
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define EB emplace_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SORT(c) sort(ALL((c)))
#define RSORT(c) sort(RALL((c)))
#define UNIQ(c) (c).erase(unique(ALL((c))), end((c)))

#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)

#define FF first
#define SS second
template <class S, class T> istream &operator>>(istream &is, pair<S, T> &p) {
  return is >> p.FF >> p.SS;
}
template <class S, class T>
ostream &operator<<(ostream &os, const pair<S, T> &p) {
  return os << p.FF << " " << p.SS;
}
template <class T> void maxi(T &x, T y) {
  if (x < y)
    x = y;
}
template <class T> void mini(T &x, T y) {
  if (x > y)
    x = y;
}

const double EPS = 1e-10;
const double PI = acos(-1.0);
const LL MOD = 1e9 + 7;

int dfs(VVI &G, int u, int p, VI &xs) {
  for (int to : G[u]) {
    if (xs[u] <= xs[to] || to == p)
      continue;
    if (!dfs(G, to, u, xs))
      return 1;
  }
  return 0;
}

int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(false);

  int N;
  cin >> N;
  VI xs(N);
  REP(i, N) cin >> xs[i];
  VVI G(N);
  REP(i, N) {
    int a, b;
    cin >> a >> b;
    --a;
    --b;
    G[a].PB(b);
    G[b].PB(a);
  }

  VI ans;
  REP(i, N) {
    if (dfs(G, i, -1, xs))
      ans.PB(i);
  }
  REP(i, SZ(ans))
  cout << (i ? " " : "") << ans[i] + 1;
  cout << endl;

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;

using VI = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;
using LL = long long;
using VL = vector<LL>;
using VVL = vector<VL>;
using PLL = pair<LL, LL>;
using VS = vector<string>;

#define ALL(a) begin((a)), end((a))
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define EB emplace_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SORT(c) sort(ALL((c)))
#define RSORT(c) sort(RALL((c)))
#define UNIQ(c) (c).erase(unique(ALL((c))), end((c)))

#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)

#define FF first
#define SS second
template <class S, class T> istream &operator>>(istream &is, pair<S, T> &p) {
  return is >> p.FF >> p.SS;
}
template <class S, class T>
ostream &operator<<(ostream &os, const pair<S, T> &p) {
  return os << p.FF << " " << p.SS;
}
template <class T> void maxi(T &x, T y) {
  if (x < y)
    x = y;
}
template <class T> void mini(T &x, T y) {
  if (x > y)
    x = y;
}

const double EPS = 1e-10;
const double PI = acos(-1.0);
const LL MOD = 1e9 + 7;

int dfs(VVI &G, int u, int p, VI &xs) {
  for (int to : G[u]) {
    if (xs[u] <= xs[to] || to == p)
      continue;
    if (!dfs(G, to, u, xs))
      return 1;
  }
  return 0;
}

int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(false);

  int N;
  cin >> N;
  VI xs(N);
  REP(i, N) cin >> xs[i];
  VVI G(N);
  REP(i, N - 1) {
    int a, b;
    cin >> a >> b;
    --a;
    --b;
    G[a].PB(b);
    G[b].PB(a);
  }

  VI ans;
  REP(i, N) {
    if (dfs(G, i, -1, xs))
      ans.PB(i);
  }
  REP(i, SZ(ans))
  cout << (i ? " " : "") << ans[i] + 1;
  cout << endl;

  return 0;
}