【題目敘述】https://zerojudge.tw/ShowProblem?problemid=a537
#include <bits/stdc++.h>
using namespace std;
int t, p[2005], cnt[123];
string s;
int main(){
p[0] = p[1] = 1;
for (int i = 2; i <= 2000; i++){
if (p[i] == 1) continue;
for (int j = i*2; j <= 2000; j += i){
p[j] = 1;
}
} //p[i] = 0 if i is prime, 0 if i is not prime
cin >> t;
for (int Case = 1; Case <= t; Case++){
cin >> s;
for (int i = 0; i <= 122; i++){
cnt[i] = 0;
}
for (int i = 0; i < s.length(); i++){
cnt[(int)(s[i])]++;
}
cout << "Case " << Case << ": ";
bool flag = false;
for (int i = 0; i <= 122; i++){ //ascii code of 'z':122
if (p[cnt[i]] == 0){
flag = true;
cout << (char)i;
}
}
if (!flag) cout << "empty";
cout << "\n";
}
}