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

#include <algorithm>
#include <bitset>
#include <cassert>
#include <climits>
#include <cmath>
#include <ctime>
#include <deque>
#include <iostream>
#include <list>
#include <map>
#include <memory.h>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;
typedef long double LD;
typedef long long LL;
typedef pair<LL, LL> pll;
typedef pair<int, int> pii;
typedef vector<int> vi;
#ifdef LOCAL
#define DEBUG(x)                                                               \\
  { cerr << "# " << #x << ": " << x << endl; }
#else
#define DEBUG(x)
#endif
mt19937_64 mt(time(0));
/*---------------------------------------------------------------------------------------------------
　　　　　　　　　　　 ∧＿∧
　　　　　 ∧＿∧ 　（´<_｀ ）　 Welcome to My Coding Space!
　　　　 （ ´_ゝ`）　/　 ⌒i
　　　　／　　　＼　 　  |　|
　　　 /　　 /￣￣￣￣/　　|
　 ＿_(__ﾆつ/　    ＿/ .| .|＿＿＿＿
　 　　　＼/＿＿＿＿/　（u　⊃
---------------------------------------------------------------------------------------------------*/
const int MAXN = 5e5 + 10;
int nums[MAXN], tree[MAXN], a[MAXN], b[MAXN], idx[MAXN], pre[MAXN], ret[MAXN];
int n;

int lowbit(int i) { return i & (-i); }
void update(int i, int val) {
  while (i <= n) {
    tree[i] += val;
    i += lowbit(i);
  }
}

int query(int i) {
  int tot = 0;
  while (i > 0) {
    tot += tree[i];
    i -= lowbit(i);
  }
  return tot;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout.precision(10);
  cout << fixed;
#ifdef LOCAL
  freopen("../test.txt", "r", stdin);
  // freopen("../output.txt", "w", stdout);
#endif
  int q;
  cin >> n >> q;
  for (int i = 1; i <= n; i++) {
    cin >> nums[i];
  }
  for (int i = 0; i < q; i++) {
    cin >> a[i] >> b[i];
    idx[i] = i;
  }
  sort(idx, idx + q, [](int i, int j) {
    return make_pair(b[i], a[i]) < make_pair(b[j], a[j]);
  });
  int cur = 1;
  for (int j = 0; j < q; j++) {
    int i = idx[j];
    while (cur <= b[i]) {
      if (pre[nums[cur]] != 0)
        update(pre[nums[cur]], -1);
      pre[nums[cur]] = cur;
      update(pre[nums[cur]], 1);
      cur++;
    }
    ret[i] = query(b[i]) - query(a[i] - 1);
  }
  for (int i = 0; i < q; i++) {
    cout << ret[i] << '\\n';
  }

/*---------------------------------------Coding Space
 * End------------------------------------------*/
#ifdef LOCAL
  cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s." << endl;
#endif
  return 0;
}
/* author:  txingml */
/* picture is from hamayanhamayan(CF handle) */


Error: TLE

Fixed submission:

#include <algorithm>
#include <bitset>
#include <cassert>
#include <climits>
#include <cmath>
#include <ctime>
#include <deque>
#include <iostream>
#include <list>
#include <map>
#include <memory.h>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;
typedef long double LD;
typedef long long LL;
typedef pair<LL, LL> pll;
typedef pair<int, int> pii;
typedef vector<int> vi;
#ifdef LOCAL
#define DEBUG(x)                                                               \\
  { cerr << "# " << #x << ": " << x << endl; }
#else
#define DEBUG(x)
#endif
mt19937_64 mt(time(0));
/*---------------------------------------------------------------------------------------------------
　　　　　　　　　　　 ∧＿∧
　　　　　 ∧＿∧ 　（´<_｀ ）　 Welcome to My Coding Space!
　　　　 （ ´_ゝ`）　/　 ⌒i
　　　　／　　　＼　 　  |　|
　　　 /　　 /￣￣￣￣/　　|
　 ＿_(__ﾆつ/　    ＿/ .| .|＿＿＿＿
　 　　　＼/＿＿＿＿/　（u　⊃
---------------------------------------------------------------------------------------------------*/
const int MAXN = 5e5 + 10;
const int block = 710;
int nums[MAXN];
int a[MAXN], b[MAXN], idx[MAXN], ret[MAXN];
map<int, int> batch[block];

void move(int x, int y, int xx, int yy, map<int, int> &table) {
  while (y < yy) {
    if (y % block == 0 && y + block <= yy) {
      for (const auto &item : batch[y / block]) {
        table[item.first] += item.second;
      }
      y += block;
    } else {
      table[nums[y]]++;
      y++;
    }
  }
  while (y > yy) {
    if (y % block == 0 && y - block >= yy) {
      for (const auto &item : batch[(y - 1) / block]) {
        auto it = table.find(item.first);
        it->second -= item.second;
        if (it->second == 0)
          table.erase(it);
      }
      y -= block;
    } else {
      y--;
      auto it = table.find(nums[y]);
      it->second--;
      if (it->second == 0)
        table.erase(it);
    }
  }
  while (x < xx) {
    if (x % block == 0 && x + block <= xx) {
      for (const auto &item : batch[x / block]) {
        auto it = table.find(item.first);
        it->second -= item.second;
        if (it->second == 0)
          table.erase(it);
      }
      x += block;
    } else {
      auto it = table.find(nums[x]);
      it->second--;
      if (it->second == 0)
        table.erase(it);
      x++;
    }
  }
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout.precision(10);
  cout << fixed;
#ifdef LOCAL
  freopen("../test.txt", "r", stdin);
  // freopen("../output.txt", "w", stdout);
#endif
  int n, q;
  cin >> n >> q;
  for (int i = 0; i < n; i++) {
    cin >> nums[i];
    batch[i / block][nums[i]]++;
  }
  for (int i = 0; i < q; i++) {
    cin >> a[i] >> b[i];
    a[i]--;
    idx[i] = i;
  }
  sort(idx, idx + q, [](int i, int j) {
    return make_pair(a[i], b[i]) < make_pair(a[j], b[j]);
  });
  int x = 0, y = 0;
  map<int, int> table;
  for (int i = 0; i < q; i++) {
    move(x, y, a[idx[i]], b[idx[i]], table);
    ret[idx[i]] = table.size();
    x = a[idx[i]];
    y = b[idx[i]];
  }
  for (int i = 0; i < q; i++) {
    cout << ret[i] << '\\n';
  }

/*---------------------------------------Coding Space
 * End------------------------------------------*/
#ifdef LOCAL
  cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s." << endl;
#endif
  return 0;
}
/* author:  txingml */
/* picture is from hamayanhamayan(CF handle) */