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

[align=left]Problem Description[/align]
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.

[align=left]Input[/align]
Multiple test cases(less than 100), for each test case, the only line indicates the positive integer
n(n≤10000).

[align=left]Output[/align]
For each test case, print the number of ways.

[align=left]Sample Input[/align]

3
9

[align=left]Sample Output[/align]

0
2

[align=left]Source[/align]
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;
}