Problem p02599 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using V = vector<int>;
using Vll = vector<ll>;
using Vld = vector<ld>;
using Vbo = vector<bool>;
using VV = vector<V>;
using VVll = vector<Vll>;
using VVld = vector<Vld>;
using VVbo = vector<Vbo>;
using VVV = vector<VV>;
using VVVll = vector<VVll>;
using P = pair<int, int>;
using Pll = pair<ll, ll>;
using Pld = pair<ld, ld>;
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define rep(i, n) rep2(i, 0, n)
#define drep(i, n) drep2(i, n, 0)
#define all(a) (a).begin(), (a).end()
struct fast_ios {
  fast_ios() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  };
} fast_ios_;
template <typename T> inline int sz(T &x) { return x.size(); }
template <typename T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << '(' << p.first << ", " << p.second << ')';
  return os;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &e : v)
    is >> e;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (auto &e : v)
    os << e << ' ';
  return os;
}
template <typename T> inline int count_between(vector<T> &a, T l, T r) {
  return lower_bound(all(a), r) - lower_bound(all(a), l);
} // [l, r)
inline int fLog2(const int x) {
  assert(x > 0);
  return 31 - __builtin_clz(x);
} // floor(log2(x))
inline int fLog2(const ll x) {
  assert(x > 0);
  return 63 - __builtin_clzll(x);
}
inline int cLog2(const int x) {
  assert(x > 0);
  return (x == 1) ? 0 : 32 - __builtin_clz(x - 1);
} // ceil(log2(x))
inline int cLog2(const ll x) {
  assert(x > 0);
  return (x == 1) ? 0 : 64 - __builtin_clzll(x - 1);
}
inline int popcount(const int x) { return __builtin_popcount(x); }
inline int popcount(const ll x) { return __builtin_popcountll(x); }
void fail() {
  puts("-1");
  exit(0);
}
// const int INF  = 1<<30;
// const ll INFll = 1ll<<62;
// const ld EPS   = 1e-10;
// const ld PI    = acos(-1.0);
// const int MOD  = int(1e9)+7;
// const int MOD  = 998244353;

int main() {
  int n, q;
  cin >> n >> q;
  V c(n);
  cin >> c;
  rep(i, n)-- c[i];
  int B = sqrt(2 * q);

  using Query = array<int, 3>;
  vector<Query> query(q);
  rep(i, q) {
    int l, r;
    cin >> l >> r;
    --l;
    query[i] = {l, r, i};
  }
  sort(all(query), [&](const Query &a, const Query &b) {
    if (a[0] / B != b[0] / B)
      return a[0] < b[0];
    else if (a[0] / B % 2 == 0)
      return a[1] < b[1];
    else
      return a[1] > b[1];
  });

  int sum = 0;
  int l = 0, r = 0;
  V cnt(n), ans(q);

  auto add = [&](int i) {
    if (cnt[c[i]] == 0)
      ++sum;
    ++cnt[c[i]];
  };
  auto del = [&](int i) {
    --cnt[c[i]];
    if (cnt[c[i]] == 0)
      --sum;
  };

  for (const auto [li, ri, i] : query) {
    while (li < l)
      add(--l);
    while (ri < r)
      del(--r);
    while (r < ri)
      add(r++);
    while (l < li)
      del(l++);
    ans[i] = sum;
  }

  cout << ans << '\\n';
  return 0;
}

Error: WA

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using V = vector<int>;
using Vll = vector<ll>;
using Vld = vector<ld>;
using Vbo = vector<bool>;
using VV = vector<V>;
using VVll = vector<Vll>;
using VVld = vector<Vld>;
using VVbo = vector<Vbo>;
using VVV = vector<VV>;
using VVVll = vector<VVll>;
using P = pair<int, int>;
using Pll = pair<ll, ll>;
using Pld = pair<ld, ld>;
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define rep(i, n) rep2(i, 0, n)
#define drep(i, n) drep2(i, n, 0)
#define all(a) (a).begin(), (a).end()
struct fast_ios {
  fast_ios() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  };
} fast_ios_;
template <typename T> inline int sz(T &x) { return x.size(); }
template <typename T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << '(' << p.first << ", " << p.second << ')';
  return os;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &e : v)
    is >> e;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (auto &e : v)
    os << e << ' ';
  return os;
}
template <typename T> inline int count_between(vector<T> &a, T l, T r) {
  return lower_bound(all(a), r) - lower_bound(all(a), l);
} // [l, r)
inline int fLog2(const int x) {
  assert(x > 0);
  return 31 - __builtin_clz(x);
} // floor(log2(x))
inline int fLog2(const ll x) {
  assert(x > 0);
  return 63 - __builtin_clzll(x);
}
inline int cLog2(const int x) {
  assert(x > 0);
  return (x == 1) ? 0 : 32 - __builtin_clz(x - 1);
} // ceil(log2(x))
inline int cLog2(const ll x) {
  assert(x > 0);
  return (x == 1) ? 0 : 64 - __builtin_clzll(x - 1);
}
inline int popcount(const int x) { return __builtin_popcount(x); }
inline int popcount(const ll x) { return __builtin_popcountll(x); }
void fail() {
  puts("-1");
  exit(0);
}
// const int INF  = 1<<30;
// const ll INFll = 1ll<<62;
// const ld EPS   = 1e-10;
// const ld PI    = acos(-1.0);
// const int MOD  = int(1e9)+7;
// const int MOD  = 998244353;

int main() {
  int n, q;
  cin >> n >> q;
  V c(n);
  cin >> c;
  rep(i, n)-- c[i];
  int B = sqrt(2 * q);

  using Query = array<int, 3>;
  vector<Query> query(n);
  rep(i, q) {
    int l, r;
    cin >> l >> r;
    l--;
    query[i] = {l, r, i};
  }
  sort(all(query), [&](const Query &a, const Query &b) {
    if (a[0] / B != b[0] / B)
      return a[0] < b[0];
    else if (a[0] / B % 2 == 0)
      return a[1] < b[1];
    else
      return a[1] > b[1];
  });

  int sum = 0;
  int l = 0, r = 0;
  V cnt(n), ans(q);

  auto add = [&](int i) {
    if (cnt[c[i]] == 0)
      ++sum;
    ++cnt[c[i]];
  };
  auto del = [&](int i) {
    --cnt[c[i]];
    if (cnt[c[i]] == 0)
      --sum;
  };

  for (const auto [li, ri, i] : query) {
    while (li < l)
      add(--l);
    while (r < ri)
      add(r++);
    while (l < li)
      del(l++);
    while (ri < r)
      del(--r);
    ans[i] = sum;
  }

  cout << ans << '\\n';
  return 0;
}