HDU5391——素数筛——Zball in Tina Town

http://acm.hdu.edu.cn/showproblem.php?pid=5391

/*
求(n-1)!%n
先打个表发现与素数有关,而且4特判，然后只要尽可能降低复杂度就行

*/
/************************************************
* Author        :Powatr
* Created Time  :2015-8-16 20:48:39
* File Name     :HDU5391.cpp
 ************************************************/

#include <cstdio>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <cstring>
#include <cmath>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <bitset>
#include <cstdlib>
#include <ctime>
using namespace std;

#define lson l, mid, rt << 1
#define rson mid + 1, r, rt << 1 | 1
typedef long long ll;
const int MAXN = 1e5 + 10;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;

int prim[MAXN] = {2};
bool is_prime(int x)
{
    for(int i = 0 ; prim[i]*prim[i] < x; i++){
        if(x % prim[i] == 0) return false;
    }
    return true;
}
int main(){
    int T, n;
    scanf("%d", &T);
    int cnt = 1;
    for(int i = 3; i <= MAXN; i++)
        if(is_prime(i))
            prim[cnt++] = i;
    while(T--){
        scanf("%d", &n);
        int i;
        if(n == 4) printf("2\n");
        else{
            if(!is_prime(n)) printf("0\n");
            else 
                printf("%d\n", n-1);
        }
    }
    return 0;
}