Language: C++

#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <string>
#include <math.h>
#include <iomanip>
#include <limits>
#include <list>
#include <queue>
#include <tuple>
#include <map>
#include <stack>
#include <set>
#include <bitset>
using namespace std;
#define fast_io ios_base::sync_with_stdio (false) ; cin.tie(0) ; cout.tie(0) ;
#define MOD (long long int)(1e9+7)
#define ll long long int
#define rep(i,n) for(int i=0; i<(int)(n); i++)
#define reps(i,n) for(int i=1; i<=(int)(n); i++)
#define REP(i,n) for(int i=n-1; i>=0; i--)
#define REPS(i,n) for(int i=n; i>0; i--)
#define INF (int)(1123456789)
#define LINF (long long int)(112345678901234567)
#define chmax(a, b) a = (((a)<(b)) ? (b) : (a))
#define chmin(a, b) a = (((a)>(b)) ? (b) : (a))
#define all(v) v.begin(), v.end()

typedef pair<int, int> Pii;
typedef pair<ll, ll> Pll;

ll mpow(ll a, ll b){
  if(b==0) return 1;
  else if(b%2==0){ll memo = mpow(a,b/2); return memo*memo%MOD;}
  else return mpow(a,b-1) * a % MOD;
}
ll lpow(ll a, ll b){
  if(b==0) return 1;
  else if(b%2==0){ll memo = lpow(a,b/2); return memo*memo;}
  else return lpow(a,b-1) * a;
}
ll gcd(ll a, ll b){
  if(b==0) return a;
  else return gcd(b, a%b);
}
vector<ll> kaijo_memo;
ll kaijo(ll n){
  if(kaijo_memo.size() > n) return kaijo_memo[n];
  if(kaijo_memo.size() == 0) kaijo_memo.push_back(1);
  while(kaijo_memo.size() <= n) kaijo_memo.push_back(kaijo_memo[kaijo_memo.size()-1] * kaijo_memo.size() % MOD);
  return kaijo_memo[n];
}
vector<ll> gyaku_kaijo_memo;
ll gyaku_kaijo(ll n){
  if(gyaku_kaijo_memo.size() > n) return gyaku_kaijo_memo[n];
  if(gyaku_kaijo_memo.size() == 0) gyaku_kaijo_memo.push_back(1);
  while(gyaku_kaijo_memo.size() <= n) gyaku_kaijo_memo.push_back(gyaku_kaijo_memo[gyaku_kaijo_memo.size()-1] * mpow(gyaku_kaijo_memo.size(), MOD-2) % MOD);
  return gyaku_kaijo_memo[n];
}

ll nCr(ll n, ll r){
  if(n == r) return 1;//0個の丸と-1個の棒みたいな時に時に効く？不安.
  if(n < r || r < 0) return 0;
  ll ret = 1;
  if(n <= 1e7){
    ret *= kaijo(n); ret %= MOD;
    ret *= gyaku_kaijo(r); ret %= MOD;
    ret *= gyaku_kaijo(n-r); ret %= MOD;
  }else{
    rep(i,r){
      ret *= n-i; ret %= MOD;
      ret *= mpow(r-i, MOD-2); ret %= MOD;
    }
  }
  return ret;
}
template< typename Monoid >
struct SegmentTree {
  using F = function< Monoid(Monoid, Monoid) >;

  int sz;
  vector< Monoid > seg;

  const F f;
  const Monoid M1;

  //SegmentTree<int> seg(N, [](int a, int b) { return min(a, b); }, INT_MAX);
  SegmentTree(int n, const F f, const Monoid &M1) : f(f), M1(M1) {
    sz = 1;
    while(sz < n) sz <<= 1;
    seg.assign(2 * sz, M1);
  }

  void set(int k, const Monoid &x) {
    seg[k + sz] = x;
  }

  void build() {
    for(int k = sz - 1; k > 0; k--) {
      seg[k] = f(seg[2 * k + 0], seg[2 * k + 1]);
    }
  }

  void update(int k, const Monoid &x) {
    k += sz;
    seg[k] = x;
    while(k >>= 1) {
      seg[k] = f(seg[2 * k + 0], seg[2 * k + 1]);
    }
  }

  Monoid query(int a, int b) {
    Monoid L = M1, R = M1;
    for(a += sz, b += sz; a < b; a >>= 1, b >>= 1) {
      if(a & 1) L = f(L, seg[a++]);
      if(b & 1) R = f(seg[--b], R);
    }
    return f(L, R);
  }

  Monoid operator[](const int &k) const {
    return seg[k + sz];
  }

  template< typename C >
  int find_subtree(int a, const C &check, Monoid &M, bool type) {
    while(a < sz) {
      Monoid nxt = type ? f(seg[2 * a + type], M) : f(M, seg[2 * a + type]);
      if(check(nxt)) a = 2 * a + type;
      else M = nxt, a = 2 * a + 1 - type;
    }
    return a - sz;
  }


  template< typename C >
  int find_first(int a, const C &check) {
    Monoid L = M1;
    if(a <= 0) {
      if(check(f(L, seg[1]))) return find_subtree(1, check, L, false);
      return -1;
    }
    int b = sz;
    for(a += sz, b += sz; a < b; a >>= 1, b >>= 1) {
      if(a & 1) {
        Monoid nxt = f(L, seg[a]);
        if(check(nxt)) return find_subtree(a, check, L, false);
        L = nxt;
        ++a;
      }
    }
    return -1;
  }

  template< typename C >
  int find_last(int b, const C &check) {
    Monoid R = M1;
    if(b >= sz) {
      if(check(f(seg[1], R))) return find_subtree(1, check, R, true);
      return -1;
    }
    int a = sz;
    for(b += sz; a < b; a >>= 1, b >>= 1) {
      if(b & 1) {
        Monoid nxt = f(seg[--b], R);
        if(check(nxt)) return find_subtree(b, check, R, true);
        R = nxt;
      }
    }
    return -1;
  }
};

int main(void){
  fast_io
  cout<<fixed<<setprecision(15);

  int n;cin>>n;
  string s; cin>>s;
  int q; cin>>q;
  vector<SegmentTree<int>> segs;
  rep(i,26){
    SegmentTree<int> seg(n+3, [](int a, int b) { return max(a, b); }, 0);
    segs.push_back(seg);
  }
  rep(i,s.size()){
    int c = s[i] - 'a';
    segs[c].update(i, 1);
  }
  rep(t,q){
    int mode;cin>>mode;
    if(mode==1){
      int i; char c;
      cin>>i>>c;i--;
      segs[s[i]-'a'].update(i,0);
      s[i] = c;
      segs[c-'a'].update(i,1);
    }else{
      int l,r;cin>>l>>r;l--;r--;
      int count = 0;
      rep(i,26){
        count += segs[i].query(l, r+1);
      }
      cout<<count<<endl;
    }
  }
  return 0;
}

Compiler output:
a.cc:80:13: error: 'function' does not name a type; did you mean 'union'?
   80 |   using F = function< Monoid(Monoid, Monoid) >;
      |             ^~~~~~~~
      |             union
a.cc:85:9: error: 'F' does not name a type
   85 |   const F f;
      |         ^
a.cc:89:28: error: 'F' does not name a type
   89 |   SegmentTree(int n, const F f, const Monoid &M1) : f(f), M1(M1) {
      |                            ^
a.cc: In constructor 'SegmentTree<Monoid>::SegmentTree(int, int, const Monoid&)':
a.cc:89:53: error: class 'SegmentTree<Monoid>' does not have any field named 'f'
   89 |   SegmentTree(int n, const F f, const Monoid &M1) : f(f), M1(M1) {
      |                                                     ^
a.cc: In function 'int main()':
a.cc:184:31: error: invalid user-defined conversion from 'main()::<lambda(int, int)>' to 'int' [-fpermissive]
  184 |     SegmentTree<int> seg(n+3, [](int a, int b) { return max(a, b); }, 0);
      |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cc:184:31: note: candidate is: 'constexpr main()::<lambda(int, int)>::operator int (*)(int, int)() const' (near match)
  184 |     SegmentTree<int> seg(n+3, [](int a, int b) { return max(a, b); }, 0);
      |                               ^
a.cc:184:31: note:   no known conversion from 'int (*)(int, int)' to 'int'
a.cc:89:30: note:   initializing argument 2 of 'SegmentTree<Monoid>::SegmentTree(int, int, const Monoid&) [with Monoid = int]'
   89 |   SegmentTree(int n, const F f, const Monoid &M1) : f(f), M1(M1) {
      |                      ~~~~~~~~^
a.cc: In instantiation of 'void SegmentTree<Monoid>::update(int, const Monoid&) [with Monoid = int]':
a.cc:189:19:   required from here
  189 |     segs[c].update(i, 1);
      |     ~~~~~~~~~~~~~~^~~~~~
a.cc:109:17: error: 'f' was not declared in this scope
  109 |       seg[k] = f(seg[2 * k + 0], seg[2 * k + 1]);
      |                ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cc: In instantiation of 'Monoid SegmentTree<Monoid>::query(int, int) [with Monoid = int]':
a.cc:203:31:   required from here
  203 |         count += segs[i].query(l, r+1);
      |                  ~~~~~~~~~~~~~^~~~~~~~
a.cc:116:22: error: 'f' was not declared in this scope
  116 |       if(a & 1) L = f(L, seg[a++]);
      |                     ~^~~~~~~~~~~~~
a.cc:117:22: error: 'f' was not declared in this scope
  117 |       if(b & 1) R = f(seg[--b], R);
      |                     ~^~~~~~~~~~~~~
a.cc:119:13: error: 'f' was not declared in this scope
  119 |     return f(L, R);
      |            ~^~~~~~