hdu 5104 Primes Problem (素数 打表 水)

http://acm.hdu.edu.cn/showproblem.php?pid=5104

 

#include<cstdio>
#include<cstring>
#include<cmath>
#include<iostream>
#include<algorithm>
using namespace std;
int isp[10000+100];
int prime[10000];
int coun;
bool isprime(int x)
{
  int i,j;
  for(i=2;i<=sqrt(x);i++)
  {
    if(x%i==0) return false;
  }
  return true;
}
void fun()
{
  int i,j;
  for(i=2;i<=10000;i++)
  {
    if(isp[i]!=0) continue;
    if(isprime(i))
    {
        isp[i]=1;
        prime[coun++]=i;
    }
    j=i;
    while(j+i<=10000)
    {
      j+=i;
      isp[j]=2;
    }
  }
}
int main()
{
  //freopen("output.txt","w",stdout);
  int ans;
  int i,j,k,n;
  memset(isp,0,sizeof(isp));
  coun=0;
  fun();
  //printf("%d...\n",coun);
  while(scanf("%d",&n)!=EOF)
  {
    int ans=0;
    for(i=0;i<coun;i++)
    {
      if(prime[i]>n/3) break;
        for(j=i;prime[j]<=(n-prime[i])/2;j++)
        {
            k=n-prime[i]-prime[j];
            if(isp[k]==1) ans++;
        }
    }
    printf("%d\n",ans);
    //n++;
  }
  return 0;
}