hint: sử dụng map  + tknp

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

void solve()
{
  long long n;
  cin >> n;
  vector<long long> a(n + 1);
  for (long long i = 1; i <= n; ++i)
  {
    cin >> a[i];
  }
  unordered_map<long long, vector<long long>> cnt;
  for (long long i = 1; i <= n; ++i)
  {
    cnt[a[i]].push_back(i);
  }
  long long q;
  cin >> q;
  while (q--)
  {
    long long k, l, r;
    cin >> k >> l >> r;

    if (cnt.find(k) == cnt.end())
    {
      cout << "0\n";
      continue;
    }
    const vector<long long> &d = cnt[k];
    auto L = lower_bound(d.begin(), d.end(), l);
    auto R = upper_bound(d.begin(), d.end(), r);
    cout << (R - L) << '\n';
  }
}

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

  int tt = 1;
  // cin >> tt;
  while (tt--)
    solve();
  return 0;
}

#danglam228

#include <bits/stdc++.h>
using namespace std;
int n, q;
const int N = 100005;
const int M = 1000005;
vector<vector<int>> f;
int main() {
    
    cin >> n;
    vector<int> a(n + 1);
    for (int i = 1; i <= n; ++i) {
        cin >> a[i];
    }
    f.resize(n + 1, vector<int>(M, 0));
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j < M; ++j) {
            f[i][j] = f[i - 1][j];
        }
        f[i][a[i]]++;
    }
    cin >> q;
    while (q--) {
        int k, l, r;
        cin >> k >> l >> r;
        cout << f[r][k] - f[l - 1][k] << '\n';
    }
    return 0;
}