Problem p02763 (C++)

Buggy submission (status: Time Limit Exceeded):
/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author champon
 */

#include <fstream>
#include <iostream>

#include <bits/stdc++.h>
#define se cout << "test ok" << endl;
#define sp << " " <<
using namespace std;
using ll = long long;
using ld = long double;
const ll mod = ll(1e9) + 7;
const ll inf = ll(5e18);
template <typename T1, typename T2> ll ceill(T1 a, T2 b) {
  return (a + b - 1) / b;
}
void ans(bool b, ostream &out = cout) { out << (b ? "Yes" : "No") << endl; }
void ans2(bool b, ostream &out = cout) { out << (b ? "YES" : "NO") << endl; }
template <typename T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  fill((T *)array, (T *)(array + N), val);
}
int dx[] = {1, 0, -1, 0, 1, -1, 1, -1};
int dy[] = {0, 1, 0, -1, 1, -1, -1, 1};

#ifndef INCLUDE_DEBUG_HPP
#define INCLUDE_DEBUG_HPP

#include <iostream>
#include <map>
#include <vector>
using namespace std;

namespace dbg {
using ll = long long;

class Debug {
public:
  Debug() {}
  template <typename T> void vd(vector<T> vec);
  template <typename T> void vd2(vector<vector<T>> vec);
  template <typename T> void ad(T *arr, ll n);
  template <typename T, size_t N> void ad2(T (&arr)[N], ll n);
  template <typename T> void md(T mp);
};

template <typename T> void Debug::vd(vector<T> vec) {
  for (auto vv : vec)
    cout << vv << " ";
  cout << endl;
}

template <typename T> void Debug::vd2(vector<vector<T>> vec) {
  for (auto vv : vec)
    for (auto vvv : vv)
      cout << vvv << " ";
  cout << endl;
}

template <typename T> void Debug::ad(T *arr, ll n) {
  for (int i = 0; i <= n; i++)
    cout << arr[i] << " ";
  cout << endl;
}

template <typename T, size_t N> void Debug::ad2(T (&arr)[N], ll n) {
  for (int i = 0; i <= N; i++)
    for (int j = 0; j <= n; j++)
      cout << arr[i][j] << " ";
  cout << endl;
}

template <typename T> void Debug::md(T mp) {
  cout << "key : value" << endl;
  for (auto const &m : mp)
    cout << m.first << " : " << m.second << endl;
  cout << endl;
}

} // namespace dbg

#endif // INCLUDE_DEBUG_HPP

using dbg::Debug;
Debug debug;

class ESimpleStringQueries {
public:
  void solve(std::istream &in, std::ostream &out) {
    ll n, q;
    string s;
    in >> n >> s >> q;
    set<int> c[26];
    for (int i = 0; i < n; i++) {
      c[s[i] - 'a'].insert(i);
    }

    for (int qi = 0; qi < q; qi++) {
      int op;
      in >> op;
      if (op == 1) {
        int iq;
        char cq;
        in >> iq >> cq;
        iq--;
        c[s[iq] - 'a'].erase(iq);
        c[cq - 'a'].insert(iq);
        s[iq] = cq;
        continue;
      }

      int l, r;
      in >> l >> r;
      l--;
      r--;
      int cnt = 0;
      for (int i = 0; i < 26; i++) {
        auto itr = lower_bound(c[i].begin(), c[i].end(), l);
        if (itr != c[i].end() && *itr <= r)
          cnt++;
      }
      out << cnt << endl;
    }
  }
};

int main() {
  ESimpleStringQueries solver;
  std::istream &in(std::cin);
  std::ostream &out(std::cout);
  solver.solve(in, out);
  return 0;
}


Fixed submission:
/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author champon
 */

#include <fstream>
#include <iostream>

#include <bits/stdc++.h>
#define se cout << "test ok" << endl;
#define sp << " " <<
using namespace std;
using ll = long long;
using ld = long double;
const ll mod = ll(1e9) + 7;
const ll inf = ll(5e18);
template <typename T1, typename T2> ll ceill(T1 a, T2 b) {
  return (a + b - 1) / b;
}
void ans(bool b, ostream &out = cout) { out << (b ? "Yes" : "No") << endl; }
void ans2(bool b, ostream &out = cout) { out << (b ? "YES" : "NO") << endl; }
template <typename T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  fill((T *)array, (T *)(array + N), val);
}
int dx[] = {1, 0, -1, 0, 1, -1, 1, -1};
int dy[] = {0, 1, 0, -1, 1, -1, -1, 1};

#ifndef INCLUDE_DEBUG_HPP
#define INCLUDE_DEBUG_HPP

#include <iostream>
#include <map>
#include <vector>
using namespace std;

namespace dbg {
using ll = long long;

class Debug {
public:
  Debug() {}
  template <typename T> void vd(vector<T> vec);
  template <typename T> void vd2(vector<vector<T>> vec);
  template <typename T> void ad(T *arr, ll n);
  template <typename T, size_t N> void ad2(T (&arr)[N], ll n);
  template <typename T> void md(T mp);
};

template <typename T> void Debug::vd(vector<T> vec) {
  for (auto vv : vec)
    cout << vv << " ";
  cout << endl;
}

template <typename T> void Debug::vd2(vector<vector<T>> vec) {
  for (auto vv : vec)
    for (auto vvv : vv)
      cout << vvv << " ";
  cout << endl;
}

template <typename T> void Debug::ad(T *arr, ll n) {
  for (int i = 0; i <= n; i++)
    cout << arr[i] << " ";
  cout << endl;
}

template <typename T, size_t N> void Debug::ad2(T (&arr)[N], ll n) {
  for (int i = 0; i <= N; i++)
    for (int j = 0; j <= n; j++)
      cout << arr[i][j] << " ";
  cout << endl;
}

template <typename T> void Debug::md(T mp) {
  cout << "key : value" << endl;
  for (auto const &m : mp)
    cout << m.first << " : " << m.second << endl;
  cout << endl;
}

} // namespace dbg

#endif // INCLUDE_DEBUG_HPP

using dbg::Debug;
Debug debug;

class ESimpleStringQueries {
public:
  void solve(std::istream &in, std::ostream &out) {
    ll n, q;
    string s;
    in >> n >> s >> q;
    set<int> c[26];
    for (int i = 0; i < n; i++) {
      c[s[i] - 'a'].insert(i);
    }

    for (int qi = 0; qi < q; qi++) {
      int op;
      in >> op;
      if (op == 1) {
        int iq;
        char cq;
        in >> iq >> cq;
        iq--;
        c[s[iq] - 'a'].erase(iq);
        c[cq - 'a'].insert(iq);
        s[iq] = cq;
        continue;
      }

      int l, r;
      in >> l >> r;
      l--;
      r--;
      int cnt = 0;
      for (int i = 0; i < 26; i++) {
        auto itr = c[i].lower_bound(l);
        if (itr != c[i].end() && *itr <= r)
          cnt++;
      }
      out << cnt << endl;
    }
  }
};

int main() {
  ESimpleStringQueries solver;
  std::istream &in(std::cin);
  std::ostream &out(std::cout);
  solver.solve(in, out);
  return 0;
}