判素数+找规律 BestCoder Round #51 (div.2) 1001 Zball in Tina Town

题目传送门

 /*
     题意： 求(n-1)! mod n
     数论：没啥意思，打个表能发现规律，但坑点是4时要特判！
 */
 /************************************************
  * Author        :Running_Time
  * Created Time  :2015-8-15 19:06:12
  * File Name     :A.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 + ;
 const int INF = 0x3f3f3f3f;
 const int MOD = 1e9 + ;

 bool is_prime(int x)    {
     if (x ==  || x == )   return true;
     if (x %  !=  && x %  != )   return false;
     for (int i=; i*i<=x; i+=) {
         if (x % i ==  || x % (i + ) == ) return false;
     }
     return true;
 }

 int main(void)    {     //BestCoder Round #51 (div.2) 1001 Zball in Tina Town
     int T;  scanf ("%d", &T);
     while (T--) {
         int n;  scanf ("%d", &n);
         if (n == ) {
             puts (""); continue;
         }
         if (is_prime (n))   {
             printf ("%d\n", n - );
         }
         else    puts ("");
     }

     return ;
 }