HDU 2161 Primes

http://acm.hdu.edu.cn/showproblem.php?pid=2161

 

Primes

Time Limit: 1000/1000 MS(Java/Others)    MemoryLimit: 32768/32768 K (Java/Others)
Total Submission(s):3191    AcceptedSubmission(s): 1298

Problem Description

Write a program to read in a list ofintegers and determine whether or not each number is prime. Anumber, n, is prime if its only divisors are 1 and n. For thisproblem, the numbers 1 and 2 are not considered primes.

 

 

Input

Each input line contains a singleinteger. The list of integers is terminated with anumber<= 0. You may assume that the input containsat most 250 numbers and each number is less than or equal to16000.

 

 

Output

The output should consists of one linefor 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 4 517 0

 

 

Sample Output

1: no 2: no3: yes 4: no 5: yes 6: yes

 

 

Source

2008 “Sunline Cup” National Invitational Contest - WarmUp

 

 

Recommend

lcy

 

题意很清楚，就是判断素数。值得注意的是：这个题目中，2不是素数；退出条件是num<=0,而非num==0.

代码如下：

#include<stdio.h>
#include<string.h>
bool prime[16001];
voidzhibiao()               //打表，效率高
{
 int i,j;
 memset(prime,1,sizeof(prime));
 prime[1]=0;
 for(i=2;i<16001;i++)
 {
  if(prime[i]==1)
   for(j=2;i*j<16001;j++)
     prime[i*j]=0;
 }
 prime[2]=0;                   //这个题目中2不是素数
}
int main()
{
 int num,m=1;
 zhibiao();
 while(scanf("%d",&num)&&num>0)       //退出条件是num<=0 这地方wrong了一次。。。
 {
  if(prime[num]==1) printf("%d:yes\n",m++);
   else printf("%d:no\n",m++);
 }
 return 0;
}