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 (Clang 3.8.0) (judge verdict: Accepted)

#include <iostream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <set>
#define fs first
#define sc second
using namespace std;
const int maxn = 5e5+10;
using pii = pair<int,int>;
typedef long long ll;

int N,Q;
string str;
struct node{
    int l,r;
    set<char> st;
}tr[maxn*4];

void pushup(node &fa,node &L,node &R){
    fa.st.clear();
    for(auto c:L.st) fa.st.insert(c);
    for(auto c:R.st) fa.st.insert(c);
}

void build(int u,int l,int r){
    if(l == r){
        tr[u] = {l,r};
        tr[u].st.insert(str[l-1]);
    }else{
        tr[u] = {l,r};
        int mid = l+r>>1;
        build(u*2,l,mid);
        build(u*2+1,mid+1,r);
        pushup(tr[u],tr[u*2],tr[u*2+1]);
    }
}
void modify(int u,int idx,char c){
    if(tr[u].l == idx && tr[u].r == idx){
        tr[u].st.clear();
        tr[u].st.insert(c);
    }else{
        int mid = (tr[u].l+tr[u].r)>>1;
        if(idx<=mid) modify(u*2,idx,c);
        else modify(u*2+1,idx,c);
        pushup(tr[u],tr[u*2],tr[u*2+1]);
    }
}
node query(int u,int l,int r){
    if(tr[u].l>=l && tr[u].r<=r){
        return tr[u];
    }else{
        int mid = (tr[u].l+tr[u].r)>>1;
        node n1,n2,n3;
        if(l<=mid) n2 = query(u*2,l,r);
        if(r>mid) n3 = query(u*2+1,l,r);
        pushup(n1,n2,n3);
        return n1;
    }
}
int main(){
    cin>>N>>str>>Q;
    build(1,1,N);
    while(Q--){
        int op,a,b;char c;
        scanf("%d",&op);
        if(op == 1){
            scanf("%d %c",&a,&c);
            modify(1,a,c);
        }else{
            scanf("%d %d",&a,&b);
            node res= query(1,a,b);
            printf("%lu\n",res.st.size());
        }
    }

    return 0;
}