hdu 3792 Twin Prime Conjecture 浙大复试上机题 水题

Twin Prime Conjecture

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 3211    Accepted Submission(s): 1138

Problem Description

If we define dn as: dn = pn+1-pn, where pi is the i-th prime. It is easy to see that d1 = 1 and dn=even for n>1. Twin Prime Conjecture states that "There are infinite consecutive primes differing by 2".
Now given any positive integer N (< 10^5), you are supposed to count the number of twin primes which are no greater than N.

 

Input

Your program must read test cases from standard input.
The input file consists of several test cases. Each case occupies a line which contains one integer N. The input is finished by a negative N.

 

Output

For each test case, your program must output to standard output. Print in one line the number of twin primes which are no greater than N.

 

Sample Input

1 5 20 -2

 

Sample Output

0 1 4

 

用筛法求素数，然后用树状数组记录区间的孪生素数对。

#include 

#define MAX 100100 

int ta[MAX*10];
int p[MAX] ;

int lowbit(int x)
{
	return x&(-x) ;
}

int sum(int x)
{
	int k = x ,sum = 0;
	while(k)
	{
		sum += ta[k] ;
		k -= lowbit(k) ;
	}
	return sum ;
}

void add(int x , int c)
{
	while(x=0)
	{
		printf("%d\n",sum(n)) ;
	}
	
	
	return 0;
}