Problem:
Score : 500 points

Problem Statement

You are given a string S of length N consisting of lowercase English letters.

Process Q queries of the following two types:

Type 1: change the i_q-th character of S to c_q. (Do nothing if the i_q-th character is already c_q.)

Type 2: answer the number of different characters occurring in the substring of S between the l_q-th and r_q-th characters (inclusive).

Constraints

N, Q, i_q, l_q, and r_q are integers.

S is a string consisting of lowercase English letters.

c_q is a lowercase English letter.

1 \leq N \leq 500000

1 \leq Q \leq 20000

|S| = N

1 \leq i_q \leq N

1 \leq l_q \leq r_q \leq N

There is at least one query of type 2 in each testcase.

Input

Input is given from Standard Input in the following format:

N
S
Q
Query_1
\vdots
Query_Q

Here, Query_i in the 4-th through (Q+3)-th lines is one of the following:

1 i_q c_q

2 l_q r_q

Output

For each query of type 2, print a line containing the answer.

Sample Input 1

7
abcdbbd
6
2 3 6
1 5 z
2 1 1
1 4 a
1 7 d
2 1 7

Sample Output 1

3
1
5

In the first query, cdbb contains three kinds of letters: b , c , and d, so we print 3.

In the second query, S is modified to abcdzbd.

In the third query, a contains one kind of letter: a, so we print 1.

In the fourth query, S is modified to abcazbd.

In the fifth query, S does not change and is still abcazbd.

In the sixth query, abcazbd contains five kinds of letters: a, b, c, d, and z, so we print 5.

Solution in C++14 (GCC 5.4.1) (judge verdict: Time Limit Exceeded)

#include <iostream>
#include <assert.h>
#include <vector>
#include <unordered_map>
#include <queue>
#include <climits>
#include <cmath>
#include <algorithm>
#include <unordered_set>
using namespace std;
constexpr int64_t MOD = 1e9 + 7;

struct segment_tree {
  int NV;
  vector<string> dat;
  segment_tree(int N, string& S) {
    NV = 1;
    while (NV < N) NV = NV << 1;
    dat.resize(NV*2 -1);
    //cout << "sg init: NV = " << NV << endl; 
    for (int i = 0; i < NV; i++) {
      dat[i+NV-1] = S[i];
    }
    for (int i = NV - 2; i >=0; i--) {
      string s = dat[i*2 + 1];
      unordered_set<char> us;
      for (int j = 0; j < (int)s.size(); j++) {
        us.emplace(s[j]);
      }
      s = dat[i*2 + 2];
      for (int j = 0; j < (int)s.size(); j++) {
        us.emplace(s[j]);
      }
      string ms = "";
      for (auto c : us) {
        ms += c;
      }
      dat[i] = ms;
    }
  }

  void update(int idx, char val) {
    //cout << "update called: " << idx << "," << val << endl;
    if (idx < 0) return;
    idx += NV - 1;
    dat[idx] = val;
    //cout << idx << ":" << dat[idx].first << "," << dat[idx].second << endl;
    while (idx > 0) {
      idx = (idx - 1) / 2;
      string s = dat[idx*2 + 1];
      unordered_set<char> us;
      for (int j = 0; j < (int)s.size(); j++) {
        us.emplace(s[j]);
      }
      s = dat[idx*2 + 2];
      for (int j = 0; j < (int)s.size(); j++) {
        us.emplace(s[j]);
      }
      string ms = "";
      for (auto c : us) {
        ms += c;
      }
      dat[idx] = ms;
      //cout << idx << ":" << dat[idx].first << "," << dat[idx].second << endl;
    }
    return;
  }

  string query(int a, int b) {
    return _query(a, b, 0, 0, NV);
  }
  string _query(int a, int b, int k, int l, int r) {
    //cout << "query called :" << a << "," << b << "," << k << "," << l << "," << r << endl;
    if (r <= a || b <= l) return "";
    if (a <= l && r <= b) return dat[k];
    else {
      string vl = _query(a, b, k*2 + 1, l, (l + r) / 2);
      string vr = _query(a, b, k*2 + 2, (l + r) / 2, r);
      unordered_set<char> us;
      for (int j = 0; j < (int)vl.size(); j++) {
        us.emplace(vl[j]);
      }
      for (int j = 0; j < (int)vr.size(); j++) {
        us.emplace(vr[j]);
      }
      string ms = "";
      for (auto c : us) {
        ms += c;
      }
      return ms;
      //cout << "querry return val: " << min(vr,vl).first << "," << min(vr,vl).second << endl;
    }
  }
};

int main(){
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);

  int32_t N, Q;
  cin >> N;
  string S;
  cin >> S;
  cin >> Q;
  
  segment_tree sg(N, S);
  vector<int> res_vect;
  for (int q = 0; q < Q; q++) {
    int type;
    cin >> type;
    int l,r;
  char c;
    if (type == 1) {
      cin >> l;
      cin >> c;
      sg.update(l-1, c);
    } else {
      cin >> l >> r;
      string qs = sg.query(l - 1, r);
      res_vect.push_back((int)qs.size());
    }
  }
  for (auto res : res_vect) {
    cout << res << endl;
  }
  return 0;
}