Modified RSQ for DCP-417

#include<bits/stdc++.h>
using namespace std;
#define mxn 100005
#define ll long long
int st[mxn*4][30];
char s[mxn], tmp[mxn];
char prv;

void build(int v, int l, int r) {
    if(l==r) {
        //st[v] = A[l];
        st[v][s[l]-'a'] = 1;
    } else {
        int m = (l+r)/2;
        build(v*2, l, m);
        build(v*2+1, m+1, r);

        //st[v] = st[v*2] + st[v*2+1];
        for(int i=0;i<26;++i) {
            st[v][i] = st[v*2][i] + st[v*2+1][i];
        }
    }
}

void update(int v, int l, int r, int id, char ch) {
    if(l==r) {
        //st[v] = val;
        st[v][s[id]-'a']=0;
        st[v][ch-'a']=1;
        return;
    }
    int m = (l+r)/2;
    if(id<=m) update(v*2, l, m, id, ch);
    else update(v*2+1, m+1, r, id, ch);

    //st[v] = st[v*2] + st[v*2+1];
    st[v][prv-'a'] = st[v*2][prv-'a'] + st[v*2+1][prv-'a'];
    st[v][ch-'a'] = st[v*2][ch-'a'] + st[v*2+1][ch-'a'];
}

int query(int v, int l, int r, int i, int j, char ch) {
    if(l>=i && r<=j) return st[v][ch-'a'];
    int m = (l+r)/2;
    if(j<=m) return query(v*2, l, m, i, j, ch);
    else if(i>m) return query(v*2+1, m+1, r, i, j, ch);
    else return query(v*2, l, m, i, m,ch) + query(v*2+1, m+1, r, m+1, j,ch);
}

int main() {
    int q, ck, id, a, x, y;
    char s1[2];
    scanf("%s",tmp);
    int n = strlen(tmp);
    for(int i=0;i<n;++i) s[i+1] = tmp[i];
    build(1,1,n);

    scanf("%d",&q);
    while(q--) {
        scanf("%d",&ck);
        if(ck==1) {
            scanf("%d %s",&id,s1);
            char ch = s1[0];
            id++;
            prv = s[id];
            update(1, 1, n, id, ch);
            s[id] = ch;
        }
        else {
            scanf("%s %d %d",s1,&x,&y);
            int ch = s1[0];
            x++, y++;
            int res = query(1,1,n,x,y,ch);
            printf("%d\n", res);
        }
    }
    return 0;
}