维护前缀和，记录每个字母出现的次数，跑一边即可

#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;
const int maxn = 1e5+5;
struct point
{
    int ch[27];
} p[maxn];
void pre(int n)
{  
    for(int i = 0; i<=26;i++)
        p[n].ch[i]=p[n-1].ch[i];
}
int work(int l, int r)
{
    int i= 0;
    
        while(p[r].ch[i]-p[l-1].ch[i]==0)
            i++;
    
    return p[r].ch[i]-p[l-1].ch[i];
}
int main()
{
    int t,n,q,l,r,c;
    scanf("%d",&t);
    for(int Ca = 1; Ca<=t;Ca++)
    {
        scanf("%d%d",&n,&q);getchar(); 
        for(int i = 1; i<=n; i++){
            
            pre(i);
            c = getchar(); 
            p[i].ch[c-'A']++;
        }
        printf("Case #%d:\n",Ca);
        for(int i = 1; i<=q; i++){
            scanf("%d%d",&l,&r);
            //if(i==q&&Ca==t)
            //    printf("%d",work(l,r));
            //else
                printf("%d\n",work(l,r));
        }
    }
    return 0;
}