Problem p02599 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;
#define LOCAL
#pragma region Macros
typedef long long ll;
#define ALL(x) (x).begin(), (x).end()
const long long MOD = 1000000007;
// const long long MOD=998244353;
const int INF = 1e9;
const long long IINF = 1e18;
const int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
const char dir[4] = {'D', 'R', 'U', 'L'};

template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (T &x : v)
    is >> x;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (int i = 0; i < v.size(); ++i) {
    os << v[i] << (i + 1 == v.size() ? "" : " ");
  }
  return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << '(' << p.first << ',' << p.second << ')';
  return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const map<T, U> &m) {
  os << '{';
  for (auto itr = m.begin(); itr != m.end(); ++itr) {
    os << '(' << itr->first << ',' << itr->second << ')';
    if (++itr != m.end())
      os << ',';
    --itr;
  }
  os << '}';
  return os;
}
template <typename T> ostream &operator<<(ostream &os, const set<T> &s) {
  os << '{';
  for (auto itr = s.begin(); itr != s.end(); ++itr) {
    os << *itr;
    if (++itr != s.end())
      os << ',';
    --itr;
  }
  os << '}';
  return os;
}

void debug_out() { cerr << '\\n'; }
template <class Head, class... Tail>
void debug_out(Head &&head, Tail &&...tail) {
  cerr << head;
  if (sizeof...(Tail) > 0)
    cerr << ", ";
  debug_out(move(tail)...);
}
#ifdef LOCAL
#define debug(...)                                                             \\
  cerr << " ";                                                                 \\
  cerr << #__VA_ARGS__ << " :[" << __LINE__ << ":" << __FUNCTION__ << "]"      \\
       << '\\n';                                                                \\
  cerr << " ";                                                                 \\
  debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

template <typename T> T gcd(T x, T y) { return y != 0 ? gcd(y, x % y) : x; }
template <typename T> T lcm(T x, T y) { return x / gcd(x, y) * y; }

template <class T1, class T2> inline bool chmin(T1 &a, T2 b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T1, class T2> inline bool chmax(T1 &a, T2 b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
#pragma endregion

struct Mo {
  int sz;
  vector<int> left, right, order;
  vector<bool> check;
  Mo(int n, int q) : sz((int)sqrt(n)), order(q), check(n) {}
  void insert(int l, int r) {
    left.emplace_back(l);
    right.emplace_back(r);
  }
  template <typename ADD, typename DEL, typename REM>
  void build(const ADD &add, const DEL &del, const REM &rem) {
    iota(order.begin(), order.end(), 0);
    sort(order.begin(), order.end(), [&](int a, int b) {
      return (left[a] / sz != left[b] / sz ? left[a] < left[b]
                                           : right[a] < right[b]);
    });
    int l = 0, r = 0;
    auto push = [&](int idx) {
      check[idx].flip();
      if (check[idx])
        add(idx);
      else
        del(idx);
    };
    for (int idx : order) {
      while (l > left[idx])
        push(--l);
      while (r < right[idx])
        push(r++);
      while (l < left[idx])
        push(l++);
      while (r > right[idx])
        push(--r);
      rem(idx);
    }
  }
};

const int MAX_N = 5e5 + 10;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int N, Q;
  cin >> N >> Q;
  vector<int> c(N);
  for (int i = 0; i < N; ++i)
    cin >> c[i];

  Mo mo(N, Q);
  for (int i = 0; i < Q; ++i) {
    int l, r;
    cin >> l >> r;
    mo.insert(--l, r);
  }
  vector<int> cnt(MAX_N, 0), ans(Q);
  int sum = 0;
  auto add = [&](int idx) {
    if (cnt[c[idx]]++ == 0)
      ++sum;
  };
  auto del = [&](int idx) {
    if (--cnt[c[idx]] == 0)
      --sum;
  };
  auto rem = [&](int idx) { ans[idx] = sum; };
  mo.build(add, del, rem);

  for (int i = 0; i < Q; ++i)
    cout << ans[i] << '\\n';
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>

using namespace std;

const int N = 500010;

int n, m, bs;
int arr[N], cnt[N], ans[N];
int curl, curr, ret;

struct query {
  int l, r, idx;
} q[N];

bool cmp(query A, query B) {
  if (A.l / bs != B.l / bs)
    return A.l / bs < B.l / bs;
  return A.r / bs < B.r / bs;
}

void add(int id) {
  cnt[arr[id]]++;
  if (cnt[arr[id]] == 1)
    ret++;
}

void remove(int id) {
  cnt[arr[id]]--;
  if (!cnt[arr[id]])
    ret--;
}

inline void inp(int &n) {
  n = 0;
  int ch = getchar_unlocked();
  int sign = 1;
  while (ch < '0' || ch > '9') {
    if (ch == '-')
      sign = -1;
    ch = getchar_unlocked();
  }
  while (ch >= '0' && ch <= '9')
    n = (n << 3) + (n << 1) + ch - '0', ch = getchar_unlocked();
  n = n * sign;
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  inp(n);
  inp(m);
  for (int i = 1; i <= n; ++i)
    inp(arr[i]);
  for (int i = 1; i <= m; ++i) {
    inp(q[i].l);
    inp(q[i].r);
    q[i].idx = i;
  }
  bs = sqrt(n);
  sort(q + 1, q + 1 + m, cmp);
  curl = 1, curr = 1;
  for (int i = 1; i <= m; ++i) {
    int lft = q[i].l, rgt = q[i].r;
    while (curl < lft) {
      remove(curl++);
    }
    while (curl > lft) {
      add(--curl);
    }
    while (curr <= rgt) {
      add(curr++);
    }
    while (curr > rgt + 1) {
      remove(--curr);
    }
    ans[q[i].idx] = ret;
  }
  for (int i = 1; i <= m; ++i)
    cout << ans[i] << '\\n';
}