hdoj-5104Primes Problem（素数打表）

Primes Problem

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 3614    Accepted Submission(s): 1629

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

39

 

Sample Output

02

 

题目链接

这里要注意素数打表和比较的方式，很容易超时。

#include<cstdio>#include<cstring>#include<algorithm>using namespace std;int num[10005];void prime(){for(int i=2;i<10005;i++){if(num[i]==0){for(int j=i+i;j<10005;j+=i)num[j]=1;}}}int main(){int n;memset(num,0,sizeof(num));num[1]=1;prime();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[j]&&!num[i]&&!num[n-i-j])ans++;}}printf("%d\n",ans);}return 0;}