Primes HDU 2161



Primes

Time Limit: 1000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 7791    Accepted Submission(s): 3195

Problem Description

Write a program to read in a list of integers and determine whether or not each number is prime. A number, n, is prime if its only divisors are 1 and n. For this problem, the numbers 1 and 2 are not considered primes.

 

Input

Each input line contains a single integer. The list of integers is terminated with a number<= 0. You may assume that the input contains at most 250 numbers and each number is less than or equal to 16000.

 

Output

The output should consists of one line for every number, where each line first lists the problem number, followed by a colon and space, followed by "yes" or "no".

 

Sample Input

   
   
   
   

    
    
    
    1
2
3
4
5
17
0
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    1: no
2: no
3: yes
4: no
5: yes
6: yes
   
   
   
   

 

判断素数问题----养成打表的好习惯

要注意这个题规定2不是素数且结束条件是n小于等于0

代码：

#include <iostream>


using namespace std;

bool primelist[17000];

void makePrimelist()
{
    int i,j;
    primelist[1]  = primelist[2] = true;
    for(i = 4;i <= 17000;i+=2)
        primelist[i] = true;

    for(i = 3;i <= 500;i+=2)
    {
        if(!primelist[i])
            for(j = i*i;j <=17000;j+=i)
            primelist[j] = true;
    }

}
int main()
{
    int n;
    int flag = 1;
    makePrimelist();
    while(cin >> n && n > 0)
    {
        if(!primelist[n]) cout << flag++ << ": yes" << endl;
        else cout << flag++ << ": no" << endl;
    }
    return 0;
}