Sieve + frequency

#include<bits/stdc++.h>
using namespace std;

bool arr[100001];
int cases;

void sieve(){
    arr[0] = true;
    arr[1] = true;
    for(int i=4;i<=100000;i+=2){
        arr[i] = true;
    }

    for(int i=3;i*i<=100000;i+=2){
        for(int j = i*i;j<=100000 ;j+=i){
            arr[j] = true;
        }
    }
}

void solve(){
    int n;
    string str;
    cin>>n>>str;

    int alpha[26]={0};

    for(int i=0;i<str.size();i++){
        alpha[str[i]-'A']++;
    }

    int co=0;

    for(int i=0; i<26;i++){
        if(!arr[alpha[i]]) co++;
    }
    printf("Case %d:\n",++cases);

    if(!co) printf("Love is painful !\n");
    else{
       for(int i=0; i<26;i++){
            if(!arr[alpha[i]]) printf("%c = %d\n",i+'A',alpha[i]);
        }
    }
}

int main(){
    sieve();

    int tc;
    cin>>tc;
    while(tc--){
        solve();
    }

}