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: Accepted)

//In The Name of Allah
#include <bits/stdc++.h>

using namespace std;

typedef long long            ll;
typedef long double          ld;
typedef string               str;
typedef pair < ll , ll >     pll;

#define X               first
#define Y               second
#define pb              push_back
#define sep             ' '
#define endl            '\n'
#define fast_io         ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define dbl_io(x)       cout << fixed << setprecision(x);
#define int long long

const int N = 5e5 + 10;
const int mod = 1e9 + 7;
const int inf = 1e18 + 10;

struct FenwickTree {
    vector<int> bit;  // binary indexed tree
    int n;

    FenwickTree(int n = N) {
        this->n = n;
        bit.assign(n, 0);
    }

    FenwickTree(vector<int> a) : FenwickTree(a.size()) {
        for (size_t i = 0; i < a.size(); i++)
            add(i, a[i]);
    }

    int sum(int r) {
        int ret = 0;
        for (; r >= 0; r = (r & (r + 1)) - 1)
            ret += bit[r];
        return ret;
    }

    int sum(int l, int r) {
        return sum(r) - sum(l - 1);
    }

    void add(int idx, int delta) {
        for (; idx < n; idx = idx | (idx + 1))
            bit[idx] += delta;
    }
};

FenwickTree A[30];

int32_t main(){
    fast_io
    //dbl_io(10);
    ll n, q;
    string s;
    cin >> n >> s >> q;
    for (ll i = 0; i < n; i ++)
        A[s[i] - 'a'].add(i, 1);
    while (q --){
        ll t;
        cin >> t;
        if (t == 1){
            ll ind;
            char x;
            cin >> ind >> x;
            ind --;
            A[s[ind] - 'a'].add(ind, -1);
            s[ind] = x;
            A[s[ind] - 'a'].add(ind, 1);
        }
        else{
            ll l, r;
            cin >> l >> r;
            l --; r --;
            ll ans = 0;
            for (ll i = 0; i < 26; i ++){
                ll res = A[i].sum(l, r);
                if (0 < res)
                    ans ++;
            }
            cout << ans << '\n';
        }
    }
    return 0;
}