hdu 1397 (素数判定)

一开始提交了这个，果断TLE

#include <cstdio>
#include <iostream>
#include <string>
#include <queue>
#include <vector>
#include <map>
#include <cmath>
using namespace std;

#define MEM(a,v) memset (a,v,sizeof(a))
// a for address, v for value

#define max(x,y) ((x)>(y)?(x):(y))
#define max(x,y) ((x)>(y)?(x):(y))

#define debug printf("!
")


bool isPrime(int n)
{
          int i;
          for(i = 3;i<=sqrtf(n);i++)
          {
                    if(n%i == 0)
                              return false;
          }
          return true;
}


int main()
{
          int n;
          int i,j;
          int count;
          while(scanf("%d",&n)!=EOF && n)
          {
                    count = 0;
                    for(i = 3;i<=n/2;i+=2)
                    {
                              if(isPrime(i))
                                        if(isPrime(n-i))
                                                  count++;
                    }
                    printf("%d
",count);
          }

          return 0;
}

看来只能打表了

#include <cstdio>
#include <iostream>
#include <string>
#include <queue>
#include <vector>
#include <map>
#include <cmath>
using namespace std;

#define MEM(a,v) memset (a,v,sizeof(a))
// a for address, v for value

#define max(x,y) ((x)>(y)?(x):(y))
#define max(x,y) ((x)>(y)?(x):(y))

#define debug printf("!
")

const int MM = 32769;

bool isPrime[MM] = {false};

void initPrime()
{
          MEM(isPrime,true);
          int i,j;

          for(i = 1;i<=MM-1;i++) if(i%2==0) isPrime[i]=false;
          for(i = 3;i<=MM/2+1;i++)
          {
                    for(j = i+i;j<=MM-1;j+=i)
                              isPrime[j] = false;
          }
          isPrime[1] = false;
          isPrime[2] = true;
}


int main()
{

          int i,n;
          initPrime();
          while(scanf("%d",&n)!=EOF && n)
          {
                    int count = 0;
                    for(i = 2;i<=n/2;i++)
                              if(isPrime[i] && isPrime[n-i])
                                        count++;
                    printf("%d
",count);
          }

          return 0;
}

421MS