4647: 【GESP2409五级】挑战怪物

#include <bits/stdc++.h>
using namespace std;
vector < int > prime;
bool is_prime[100010];
void Eratosthenes(int n) {
    is_prime[0] = is_prime[1] = false;
    for (int i = 2; i <= n; ++i) is_prime[i] = true;
    for (int i = 2; i <= n; ++i) {
        if (is_prime[i]) {
            prime.push_back(i);
            if ((long long) i * i > n) continue;
            for (int j = i * i; j <= n; j += i)
                is_prime[j] = false;
        }
    }
}
int main() {
    Eratosthenes(100000);
    int t;
    cin >> t;
    while (t--) {
        int tmp = 1;
        int x;
        cin >> x;
        int ans = 0;
        while (1) {
            if (is_prime[x]) {
                ans++;
                break;
            }
            x -= tmp;
            ans++;
            if (x <= 0) {
                if (x < 0) ans = -1;
                break;
            }
            tmp *= 2;
        }
        cout << ans << "\n";
    }
}