Language: C++

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using VI = vector<int>;
using VL = vector<ll>;
using VS = vector<string>;
template<class T> using PQ = priority_queue<T, vector<T>, greater<T>>;
#define FOR(i,a,n) for(int (i)=(a);(i)<(n);++(i))
#define eFOR(i,a,n) for(int (i)=(a);(i)<=(n);++(i))
#define rFOR(i,a,n) for(int (i)=(n)-1;(i)>=(a);--(i))
#define erFOR(i,a,n) for(int (i)=(n);(i)>=(a);--(i))
#define each(i, a) for(auto &i : a)
#define SORT(i) sort((i).begin(),(i).end())
#define rSORT(i,a) sort((i).begin(),(i).end(),(a))
#define all(i) (i).begin(),(i).end()
#define out(y,x) ((y) < 0 || h <= (y) || (x) < 0 || w <= (x))
#define line cout << "-----------------------------\n" 
#define ENDL(i,n) ((i) == (n) - 1 ? "\n" : " ")
#define stop system("pause")
constexpr ll INF = 1000000000;
constexpr ll LLINF = 1LL << 60;
constexpr ll mod = 1000000007;
constexpr ll MOD = 998244353;
constexpr ld eps = 1e-10;
constexpr ld pi = 3.1415926535897932;
template<class T>inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; }return false; }
template<class T>inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; }return false; }
inline void init() { cin.tie(nullptr); cout.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); }
template<class T>inline istream& operator>>(istream& is, vector<T>& v) { for (auto& elemnt : v)is >> elemnt; return is; }
template<class T>inline istream& operator>>(istream& is, deque<T>& v) { for (auto& elemnt : v)is >> elemnt; return is; }
template<class T, class U>inline istream& operator>>(istream& is, pair<T, U>& p) { is >> p.first >> p.second; return is; }
template<class T>inline vector<T> vec(size_t a) { return vector<T>(a); }
template<class T>inline vector<T> defvec(T def, size_t a) { return vector<T>(a, def); }
template<class T, class... Ts>inline auto vec(size_t a, Ts... ts) { return vector<decltype(vec<T>(ts...))>(a, vec<T>(ts...)); }
template<class T, class... Ts>inline auto defvec(T def, size_t a, Ts... ts) { return vector<decltype(defvec<T>(def, ts...))>(a, defvec<T>(def, ts...)); }

#include<bits/stdc++.h>
using namespace std;
#define FOR(i,a,n) for(int i=(a);i<(n);++i)
#define rFOR(i,a,n) for(int i=(n)-1;(a)<=i;--i)
template<class T> class segtree {
	int n = 1;
	vector<T> dat;
	T def;
public:
	segtree(const vector<T>& _dat, const T _def = 0) : def(_def) {
		int _n = _dat.size();
		while (n < _n)n <<= 1;
		dat.resize(n << 1, def);
		FOR(i, 0, _n)dat[i + n] = _dat[i];
		rFOR(i, 1, n)dat[i] = dat[i << 1] | dat[i << 1 | 1];
	}
	void update(int i, T a) {
		i += n;
		dat[i] = a;
		while (1 < i) {
			i >>= 1;
			dat[i] = dat[i << 1] | dat[i << 1 | 1];
		}
	}
	T value(int l, int r) {
		T ret = def;
		for (l += n, r += n; l < r; l >>= 1, r >>= 1) {
			if (l & 1)ret |= dat[l++];
			if (r & 1)ret |= dat[--r];
		}
		return ret;
	}
};

int main() {
	int n; cin >> n;
	string s; cin >> s;
	int q; cin >> q;

	vector<int> a(n);
	FOR(i, 0, n)a[i] = 1 << (s[i] - 'a');
	segtree<int> seg(a);

	while (q--) {
		int t; cin >> t;
		if (t == 1) {
			int i; char c; cin >> i >> c;
			seg.update(i - 1, 1 << (c - 'a'));
		}
		else {
			int l, r; cin >> l >> r;
			int b = seg.value(l - 1, r);
			int ans = 0;
			FOR(i, 0, 26)if (b & (1 << i))++ans;
			cout << ans << "\n";
		}
	}
}


int main() {
	init();

	int n; cin >> n;
	string s; cin >> s;
	int q; cin >> q;

	vector<int> a(n);
	FOR(i, 0, n)a[i] = 1 << (s[i] - 'a');
	segtree<int> seg(a);

	while (q--) {
		int t; cin >> t;
		if (t == 1) {
			int i; char c; cin >> i >> c;
			seg.update(i - 1, 1 << (c - 'a'));
		}
		else {
			int l, r; cin >> l >> r;
			int b = seg.value(l - 1, r);
			int ans = 0;
			FOR(i, 0, 26)if (b & (1 << i))++ans;
			cout << ans << "\n";
		}
	}
}

Compiler output:
a.cc:40:9: warning: "FOR" redefined
   40 | #define FOR(i,a,n) for(int i=(a);i<(n);++i)
      |         ^~~
a.cc:9:9: note: this is the location of the previous definition
    9 | #define FOR(i,a,n) for(int (i)=(a);(i)<(n);++(i))
      |         ^~~
a.cc:41:9: warning: "rFOR" redefined
   41 | #define rFOR(i,a,n) for(int i=(n)-1;(a)<=i;--i)
      |         ^~~~
a.cc:11:9: note: this is the location of the previous definition
   11 | #define rFOR(i,a,n) for(int (i)=(n)-1;(i)>=(a);--(i))
      |         ^~~~
a.cc:98:5: error: redefinition of 'int main()'
   98 | int main() {
      |     ^~~~
a.cc:72:5: note: 'int main()' previously defined here
   72 | int main() {
      |     ^~~~