hdoj--5104--Primes Problem(素数打表)

Primes Problem

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)

Total Submission(s): 2016    Accepted Submission(s): 928

Problem Description

Given a number n, please count how many tuple(p1, p2, p3) satisfied that p1<=p2<=p3, p1,p2,p3 are primes and p1 + p2 + p3 = n.

 

Input

Multiple test cases(less than 100), for each test case, the only line indicates the positive integer
n(n≤10000).

 

Output

For each test case, print the number of ways.

 

Sample Input

3
9

 

Sample Output

0
2

 

Source

BestCoder Round #18

给出n，计算三个素数相加等于n的方案个数，素数打表就行

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int num[10020];
void prim()
{
	for(int i=2;i<10020;i++)
	{
		if(num[i]==0)
		{
			for(int j=i+i;j<10020;j+=i)
			num[j]=1;
		}
	}
}
int main()
{
	int n;
	memset(num,0,sizeof(num));
	num[1]=1;
	prim();
	while(scanf("%d",&n)!=EOF)
	{
		int ans=0;
		for(int i=2;i<=n;i++)
		{
			for(int j=i;j<=(n-i)/2;j++)
			{
				if(!num[i]&&!num[j]&&!num[n-i-j])
				ans++;
			}
		}
		printf("%d\n",ans);
	}
	return 0;
}