HDOJ(HDU) 2161 Primes(素数打表)

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

给你一个数，判断它是不是素数，是素数输出**: yes,不是就输出

**: no

注意：1和2要输出no。

还有，判断结束的标志是n<=0.

import java.util.Arrays;
import java.util.Scanner;

public class Main{
    static boolean db[] = new boolean[16001];
    public static void main(String[] args) {
        prime();
        Scanner sc = new Scanner(System.in);
        int t=0;
        while(sc.hasNext()){
            int n =sc.nextInt();
            if(n<=0){
                break;
            }
            if(db[n]){
                System.out.println((++t)+": yes");
            }else{
                System.out.println((++t)+": no");
            }
        }
    }
    private static void prime() {
        Arrays.fill(db, true);
        db[1]=false;
        db[2]=false;
        for(int i=2;i<=Math.sqrt(db.length);i++){
            for(int j=i+i;j<db.length;j+=i){
                if(db[j]){
                    db[j]=false;
                }
            }
        }
    }
}