Problem p02763 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define countof(array) (sizeof(array) / sizeof(array[0]))
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = (n)-1; i >= 0; --i)
#define rep2(i, n) for (int i = 1; i <= (n); ++i)
#define rrep2(i, n) for (int i = (n); i > 0; --i)
#define srep(i, s, n) for (int i = s; i < (n); ++i)
#define rsrep(i, s, n) for (int i = (n)-1; i >= s; --i)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define aall(a) (a), (a) + countof(a) // for array sorting
#define raall(a) (a), (a) + countof(a), greater<>()
#define show(x) cout << #x << " = " << (x) << endl;
#define vfind(v, a) find(all(v), a) != v.end()
#define yn(f)                                                                  \
  {                                                                            \
    if (f)                                                                     \
      puts("YES");                                                             \
    else                                                                       \
      puts("NO");                                                              \
  }
#define yns(f)                                                                 \
  {                                                                            \
    if (f)                                                                     \
      puts("Yes");                                                             \
    else                                                                       \
      puts("No");                                                              \
  }
#define show_ary(...)                                                          \
  {                                                                            \
    cout << #__VA_ARGS__ << " = ";                                             \
    for (const auto &x : (__VA_ARGS__)) {                                      \
      cout << x << " ";                                                        \
    }                                                                          \
    cout << endl;                                                              \
  }
#define show_pair(...)                                                         \
  cout << #__VA_ARGS__ << " = " << endl;                                       \
  for (const auto &x : (__VA_ARGS__)) {                                        \
    cout << "  " << x.fi << " : " << x.se << endl;                             \
  }
#define out_ary(...)                                                           \
  {                                                                            \
    int n = (__VA_ARGS__).size();                                              \
    rep(i, n) printf("%d%s", (__VA_ARGS__)[i], i != n - 1 ? " " : "\n");       \
  }
#define argmax(v) distance((v).begin(), max_element(all(v)))
#define argmin(v) distance((v).begin(), min_element(all(v)))
#define vmax(v) *max_element(all(v))
#define vmin(v) *min_element(all(v))
typedef long long int ll;
typedef pair<int, int> P;
typedef vector<P> vpair;
typedef vector<int> vint;
typedef vector<ll> vll;
typedef vector<double> vdouble;
typedef vector<string> vstr;
typedef vector<bool> vbool;
typedef vector<vint> vvint;
typedef vector<vll> vvll;
typedef vector<vstr> vvstr;
typedef vector<vbool> vvbool;
const ll LINF = 2000000000000000000ll;
const int INF = 1000000100;
const ll MOD = 1e9 + 7;

int main() {
  int n;
  string s;
  int q;
  cin >> n >> s >> q;
  int sl = s.length();
  vector<set<int>> st(26);

  rep(i, sl) { st[s[i] - 'a'].insert(i); }

  rep(i, q) {
    int a;
    cin >> a;
    if (a == 1) {
      int b;
      char c;
      cin >> b >> c;
      --b;
      st[s[b] - 'a'].erase(b);
      st[c - 'a'].insert(b);
      s[b] = c;
    } else {
      int l, r;
      cin >> l >> r;
      --l;
      int ans = 0;
      for (auto sti : st) {
        auto id = sti.lower_bound(l);
        if (sti.end() != id && *id < r)
          ans++;
      }
      cout << ans << endl;
    }
  }

  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define countof(array) (sizeof(array) / sizeof(array[0]))
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = (n)-1; i >= 0; --i)
#define rep2(i, n) for (int i = 1; i <= (n); ++i)
#define rrep2(i, n) for (int i = (n); i > 0; --i)
#define srep(i, s, n) for (int i = s; i < (n); ++i)
#define rsrep(i, s, n) for (int i = (n)-1; i >= s; --i)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define aall(a) (a), (a) + countof(a) // for array sorting
#define raall(a) (a), (a) + countof(a), greater<>()
#define show(x) cout << #x << " = " << (x) << endl;
#define vfind(v, a) find(all(v), a) != v.end()
#define yn(f)                                                                  \
  {                                                                            \
    if (f)                                                                     \
      puts("YES");                                                             \
    else                                                                       \
      puts("NO");                                                              \
  }
#define yns(f)                                                                 \
  {                                                                            \
    if (f)                                                                     \
      puts("Yes");                                                             \
    else                                                                       \
      puts("No");                                                              \
  }
#define show_ary(...)                                                          \
  {                                                                            \
    cout << #__VA_ARGS__ << " = ";                                             \
    for (const auto &x : (__VA_ARGS__)) {                                      \
      cout << x << " ";                                                        \
    }                                                                          \
    cout << endl;                                                              \
  }
#define show_pair(...)                                                         \
  cout << #__VA_ARGS__ << " = " << endl;                                       \
  for (const auto &x : (__VA_ARGS__)) {                                        \
    cout << "  " << x.fi << " : " << x.se << endl;                             \
  }
#define out_ary(...)                                                           \
  {                                                                            \
    int n = (__VA_ARGS__).size();                                              \
    rep(i, n) printf("%d%s", (__VA_ARGS__)[i], i != n - 1 ? " " : "\n");       \
  }
#define argmax(v) distance((v).begin(), max_element(all(v)))
#define argmin(v) distance((v).begin(), min_element(all(v)))
#define vmax(v) *max_element(all(v))
#define vmin(v) *min_element(all(v))
typedef long long int ll;
typedef pair<int, int> P;
typedef vector<P> vpair;
typedef vector<int> vint;
typedef vector<ll> vll;
typedef vector<double> vdouble;
typedef vector<string> vstr;
typedef vector<bool> vbool;
typedef vector<vint> vvint;
typedef vector<vll> vvll;
typedef vector<vstr> vvstr;
typedef vector<vbool> vvbool;
const ll LINF = 2000000000000000000ll;
const int INF = 1000000100;
const ll MOD = 1e9 + 7;

int main() {
  int n;
  string s;
  int q;
  cin >> n >> s >> q;
  int sl = s.length();
  vector<set<int>> st(26);

  rep(i, sl) { st[s[i] - 'a'].insert(i); }

  rep(i, q) {
    int a;
    cin >> a;
    if (a == 1) {
      int b;
      char c;
      cin >> b >> c;
      --b;
      st[s[b] - 'a'].erase(b);
      st[c - 'a'].insert(b);
      s[b] = c;
    } else {
      int l, r;
      cin >> l >> r;
      --l;
      int ans = 0;
      // for (auto sti : st) {
      //     auto id = sti.lower_bound(l);
      //     if (sti.end() != id && *id < r) ans++;
      // }
      rep(j, 26) {
        auto id = st[j].lower_bound(l);
        if (st[j].end() != id && *id < r)
          ans++;
      }
      cout << ans << endl;
    }
  }

  return 0;
}