Problem p02763 (C++)

Buggy submission (status: Runtime Error):
/*input
abcdefgh
4
1 2 a
1 8 g
2 1 3
2 1 8

*/

/*
                                                    ______________
                                                          |       )
                                                          |   )   /
                                                          |______/
                                                    |     |      \
                                                    |     |   )   \
                                                    |_____|_______)

*/
#include <algorithm>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
typedef long double ld;

#define pb push_back
#define all(c) c.begin(), c.end()
#define allr(c) c.rbegin(), c.rend()
int mod = 1000000007;
const int inf = 1034567891;
const ll LL_INF = 1234567890123456789ll;
#define PI 3.14159265
#define endl '\n'
#define F first
#define S second
#define debug(x) cout << #x << " = " << x << endl;
#define TRACE

#ifdef TRACE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cout << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cout.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
#else
#define trace(...)
#endif

#define out(container)                                                         \
  for (auto it : container)                                                    \
    cout << it << " ";                                                         \
  cout << endl;

template <typename T> T GCD(T a, T b) {
  ll t;
  while (a) {
    t = a;
    a = b % a;
    b = t;
  }
  return b;
}
template <typename T> string toString(T a) { return to_string(a); }
template <typename T> void toInt(string s, T &x) {
  stringstream str(s);
  str >> x;
}
inline int add(int x, int y) {
  x += y;
  if (x >= mod)
    x -= mod;
  return x;
}
inline int sub(int x, int y) {
  x -= y;
  if (x < 0)
    x += mod;
  return x;
}
inline int mul(int x, int y) { return (x * 1ll * y) % mod; }
inline int powr(int a, ll b) {
  int x = 1 % mod;
  while (b) {
    if (b & 1)
      x = mul(x, a);
    a = mul(a, a);
    b >>= 1;
  }
  return x;
}
inline int inv(int a) { return powr(a, mod - 2); }

const int N = 1e5 + 5;
int bit[26][N];

void update(int w, int ind, int val) {
  for (; ind < N; ind += (ind & -ind)) {
    bit[w][ind] += val;
  }
}
int query(int w, int ind) {
  int ans = 0;
  for (; ind > 0; ind -= (ind & -ind)) {
    ans += bit[w][ind];
  }
  return ans;
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int ghj;
  cin >> ghj;
  string str;
  cin >> str;
  int n = str.size();
  str = '#' + str;
  for (int i = 1; i <= n; i++) {
    update(str[i] - 'a', i, 1);
  }
  int q;
  cin >> q;
  while (q--) {
    int type;
    cin >> type;
    if (type == 1) {
      int ind;
      char c;
      cin >> ind >> c;
      int w = c - 'a';
      update(str[ind] - 'a', ind, -1);
      update(w, ind, 1);
      str[ind] = c;
    } else {
      int l, r;
      cin >> l >> r;
      int ans = 0;
      for (int i = 0; i < 26; i++) {
        int c = query(i, r) - query(i, l - 1);
        ans += (c >= 1);
      }
      cout << ans << endl;
    }
  }

  return 0;
}

Fixed submission:
/*input
abcdefgh
4
1 2 a
1 8 g
2 1 3
2 1 8

*/

/*
                                                    ______________
                                                          |       )
                                                          |   )   /
                                                          |______/
                                                    |     |      \
                                                    |     |   )   \
                                                    |_____|_______)

*/
#include <algorithm>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
typedef long double ld;

#define pb push_back
#define all(c) c.begin(), c.end()
#define allr(c) c.rbegin(), c.rend()
int mod = 1000000007;
const int inf = 1034567891;
const ll LL_INF = 1234567890123456789ll;
#define PI 3.14159265
#define endl '\n'
#define F first
#define S second
#define debug(x) cout << #x << " = " << x << endl;
#define TRACE

#ifdef TRACE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cout << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cout.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
#else
#define trace(...)
#endif

#define out(container)                                                         \
  for (auto it : container)                                                    \
    cout << it << " ";                                                         \
  cout << endl;

template <typename T> T GCD(T a, T b) {
  ll t;
  while (a) {
    t = a;
    a = b % a;
    b = t;
  }
  return b;
}
template <typename T> string toString(T a) { return to_string(a); }
template <typename T> void toInt(string s, T &x) {
  stringstream str(s);
  str >> x;
}
inline int add(int x, int y) {
  x += y;
  if (x >= mod)
    x -= mod;
  return x;
}
inline int sub(int x, int y) {
  x -= y;
  if (x < 0)
    x += mod;
  return x;
}
inline int mul(int x, int y) { return (x * 1ll * y) % mod; }
inline int powr(int a, ll b) {
  int x = 1 % mod;
  while (b) {
    if (b & 1)
      x = mul(x, a);
    a = mul(a, a);
    b >>= 1;
  }
  return x;
}
inline int inv(int a) { return powr(a, mod - 2); }

const int N = 7e5 + 5;
int bit[26][N];

void update(int w, int ind, int val) {
  for (; ind < N; ind += (ind & -ind)) {
    bit[w][ind] += val;
  }
}
int query(int w, int ind) {
  int ans = 0;
  for (; ind > 0; ind -= (ind & -ind)) {
    ans += bit[w][ind];
  }
  return ans;
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int ghj;
  cin >> ghj;
  string str;
  cin >> str;
  int n = str.size();
  str = '#' + str;
  for (int i = 1; i <= n; i++) {
    update(str[i] - 'a', i, 1);
  }
  int q;
  cin >> q;
  while (q--) {
    int type;
    cin >> type;
    if (type == 1) {
      int ind;
      char c;
      cin >> ind >> c;
      int w = c - 'a';
      update(str[ind] - 'a', ind, -1);
      update(w, ind, 1);
      str[ind] = c;
    } else {
      int l, r;
      cin >> l >> r;
      int ans = 0;
      for (int i = 0; i < 26; i++) {
        int c = query(i, r) - query(i, l - 1);
        ans += (c >= 1);
      }
      cout << ans << endl;
    }
  }

  return 0;
}