Problem p02689 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define M1 1000000007
#define M2 998244353
#define ll long long int
#define pll pair<ll, ll>
#define mll map<ll, ll>
#define F first
#define S second
#define PB push_back
#define mp make_pair
#define lb lower_bound
#define ub upper_bound
#define V(a) vector<a>
#define endl '\\n'
#define test(t) while (t--)
#define PI acos(-1.0)
#define rep(i, a, b) for (ll i = a; i < b; i++)
#define repp(i, b, a) for (ll i = b - 1; i >= a; i--)
#define clr(ar, val) memset(ar, val, sizeof(ar))
#define setbits(x) __builtin_popcountll(x)
#define zrobits(x) __builtin_ctzll(x)
#define ps(y) fixed << setprecision(y)
#define all(x) begin(x), end(x)
#define allr(x) rbegin(x), rend(x)
const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3f;
const int dx[4] = {0, -1, 0, 1};
const int dy[4] = {-1, 0, 1, 0};

unsigned int randInt() {
  static unsigned int tx = 123456789, ty = 362436069, tz = 521288629,
                      tw = 88675123;
  unsigned int tt = (tx ^ (tx << 11));
  tx = ty;
  ty = tz;
  tz = tw;
  return (tw = (tw ^ (tw >> 19)) ^ (tt ^ (tt >> 8)));
}

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template <typename T>
#define o_set(T)                                                               \\
  tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>
// member functions :
// 1. order_of_key(k) : number of elements strictly lesser than k
// 2. find_by_order(k) : k-th element in the set

ll floor_div(ll a, ll b) {
  return a / b - (((a ^ b) < 0) and a % b);
}
ll ceil_div(ll a, ll b) { return a / b + (((a ^ b) >= 0) and a % b); }

vector<int> suffix_array_cyclic(string s) {
  int n = s.size(), N = n + 256;
  vector<int> sa(n), ra(n);
  for (int i = 0; i < n; i++)
    sa[i] = i, ra[i] = s[i];
  for (int k = 0; k < n; k ? k *= 2 : k++) {
    vector<int> nsa(sa), nra(n), cnt(N);
    for (int i = 0; i < n; i++)
      nsa[i] = (nsa[i] - k + n) % n;
    for (int i = 0; i < n; i++)
      cnt[ra[i]]++;
    for (int i = 1; i < N; i++)
      cnt[i] += cnt[i - 1];
    for (int i = n - 1; i >= 0; i--)
      sa[--cnt[ra[nsa[i]]]] = nsa[i];

    int r = 0;
    for (int i = 1; i < n; i++) {
      if (ra[sa[i]] != ra[sa[i - 1]])
        r++;
      else if (ra[(sa[i] + k) % n] != ra[(sa[i - 1] + k) % n])
        r++;
      nra[sa[i]] = r;
    }
    ra = nra;
  }
  return sa;
}

vector<int> kasai(string s, vector<int> sa) {
  int n = s.size(), k = 0;
  vector<int> ra(n), lcp(n);
  for (int i = 0; i < n; i++)
    ra[sa[i]] = i;
  for (int i = 0; i < n; i++) {
    if (k)
      k--;
    if (ra[i] == n - 1) {
      k = 0;
      continue;
    }
    int j = sa[ra[i] + 1];
    while (k < n && s[(i + k) % n] == s[(j + k) % n])
      k++;
    lcp[ra[i]] = k;
    if (ra[(sa[ra[i]] + 1) % n] > ra[(sa[ra[j]] + 1) % n])
      k = 0;
  }
  return lcp;
}

inline void INP() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
}
ll height[100005];
V(ll) adj[100005];
ll good = 0;
void solve() {
  ll n, m;
  cin >> n >> m;
  rep(i, 1, n + 1) cin >> height[i];
  rep(i, 0, m) {
    ll x, y;
    cin >> x >> y;
    if (find(all(adj[x]), y) == adj[x].end()) {
      adj[x].PB(y);
      adj[y].PB(x);
    }
  }
  rep(i, 1, n + 1) {
    bool flag = 1;
    for (ll j : adj[i]) {
      if (height[j] >= height[i]) {
        flag = 0;
        break;
      }
    }
    if (flag)
      good++;
  }
  cout << good;
}

int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  // cin>>t;
  test(t) { solve(); }
  return 0;
}

Error: WA

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define M1 1000000007
#define M2 998244353
#define ll long long int
#define pll pair<ll, ll>
#define mll map<ll, ll>
#define F first
#define S second
#define PB push_back
#define mp make_pair
#define lb lower_bound
#define ub upper_bound
#define V(a) vector<a>
#define endl '\\n'
#define test(t) while (t--)
#define PI acos(-1.0)
#define rep(i, a, b) for (ll i = a; i < b; i++)
#define repp(i, b, a) for (ll i = b - 1; i >= a; i--)
#define clr(ar, val) memset(ar, val, sizeof(ar))
#define setbits(x) __builtin_popcountll(x)
#define zrobits(x) __builtin_ctzll(x)
#define ps(y) fixed << setprecision(y)
#define all(x) begin(x), end(x)
#define allr(x) rbegin(x), rend(x)
const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3f;
const int dx[4] = {0, -1, 0, 1};
const int dy[4] = {-1, 0, 1, 0};

unsigned int randInt() {
  static unsigned int tx = 123456789, ty = 362436069, tz = 521288629,
                      tw = 88675123;
  unsigned int tt = (tx ^ (tx << 11));
  tx = ty;
  ty = tz;
  tz = tw;
  return (tw = (tw ^ (tw >> 19)) ^ (tt ^ (tt >> 8)));
}

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template <typename T>
#define o_set(T)                                                               \\
  tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>
// member functions :
// 1. order_of_key(k) : number of elements strictly lesser than k
// 2. find_by_order(k) : k-th element in the set

ll floor_div(ll a, ll b) {
  return a / b - (((a ^ b) < 0) and a % b);
}
ll ceil_div(ll a, ll b) { return a / b + (((a ^ b) >= 0) and a % b); }

vector<int> suffix_array_cyclic(string s) {
  int n = s.size(), N = n + 256;
  vector<int> sa(n), ra(n);
  for (int i = 0; i < n; i++)
    sa[i] = i, ra[i] = s[i];
  for (int k = 0; k < n; k ? k *= 2 : k++) {
    vector<int> nsa(sa), nra(n), cnt(N);
    for (int i = 0; i < n; i++)
      nsa[i] = (nsa[i] - k + n) % n;
    for (int i = 0; i < n; i++)
      cnt[ra[i]]++;
    for (int i = 1; i < N; i++)
      cnt[i] += cnt[i - 1];
    for (int i = n - 1; i >= 0; i--)
      sa[--cnt[ra[nsa[i]]]] = nsa[i];

    int r = 0;
    for (int i = 1; i < n; i++) {
      if (ra[sa[i]] != ra[sa[i - 1]])
        r++;
      else if (ra[(sa[i] + k) % n] != ra[(sa[i - 1] + k) % n])
        r++;
      nra[sa[i]] = r;
    }
    ra = nra;
  }
  return sa;
}

vector<int> kasai(string s, vector<int> sa) {
  int n = s.size(), k = 0;
  vector<int> ra(n), lcp(n);
  for (int i = 0; i < n; i++)
    ra[sa[i]] = i;
  for (int i = 0; i < n; i++) {
    if (k)
      k--;
    if (ra[i] == n - 1) {
      k = 0;
      continue;
    }
    int j = sa[ra[i] + 1];
    while (k < n && s[(i + k) % n] == s[(j + k) % n])
      k++;
    lcp[ra[i]] = k;
    if (ra[(sa[ra[i]] + 1) % n] > ra[(sa[ra[j]] + 1) % n])
      k = 0;
  }
  return lcp;
}

inline void INP() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
}
ll height[100005];
V(ll) adj[100005];
ll good = 0;
map<ll, bool> visited;
void dfs(ll node, ll parent) {
  visited[node] = 1;
  bool flag = 1;
  for (ll c : adj[node]) {
    if (height[c] >= height[node]) {
      flag = 0;
      break;
    }
  }
  for (ll c : adj[node]) {
    if (c != parent) {
      dfs(c, node);
    }
  }
  if (flag)
    good++;
}
void solve() {
  ll n, m;
  cin >> n >> m;
  rep(i, 1, n + 1) cin >> height[i];
  rep(i, 0, m) {
    ll x, y;
    cin >> x >> y;
    if (find(all(adj[x]), y) == adj[x].end()) {
      adj[x].PB(y);
      adj[y].PB(x);
    }
  }
  rep(i, 1, n + 1) {
    if (!visited[i]) {
      dfs(i, -1);
    }
  }
  cout << good;
}

int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  // cin>>t;
  test(t) { solve(); }
  return 0;
}