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;

}

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