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  • 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
    ");
            else{
                if(!is_prime(n)) printf("0
    ");
                else 
                    printf("%d
    ", n-1);
            }
        }
        return 0;
    }
    

      

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  • 原文地址:https://www.cnblogs.com/zero-begin/p/4735007.html
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