Fermat’s Chirstmas Theorem (素数打表的)
Description
In a letter dated December 25, 1640; the great mathematician Pierre de Fermat wrote to Marin Mersenne that he just proved that an odd prime p is expressible as p = a2 + b2 if and only if p is expressible as p = 4c + 1. As usual, Fermat didn’t include the proof, and as far as we know, never
wrote it down. It wasn’t until 100 years later that no one other than Euler proved this theorem.
Input
Your program will be tested on one or more test cases. Each test case is specified on a separate input line that specifies two integers L, U where L ≤ U < 1, 000, 000
The last line of the input file includes a dummy test case with both L = U = −1.
Output
L U x y
where L and U are as specified in the input. x is the total number of primes within the interval [L, U ] (inclusive,) and y is the total number of primes (also within [L, U ]) that can be expressed as a sum of squares.
Sample Input
10 20 11 19 100 1000 -1 -1
Sample Output
10 20 4 2 11 19 4 2 100 1000 143 69
#include<stdio.h>
#include<string.h>
#define N 1000005
int prime[100005];
int flag[1000005];
int e;
void getP() // 素数打表,找出素数存栈
{
int i, j;
e = 0;
memset(flag, 0, sizeof(flag) ); //标记初始化
for ( i=2; i<N; i++)
{
if ( flag[i]==0 )
{
prime[e++] = i; //进栈
}
for ( j=0; j<e && i*prime[j]<N; j++ )
{
flag[ i * prime[j] ] = 1;
}
}
}
int main()
{
int l,u,x,y;
getP();
int i;
while(scanf("%d %d",&l,&u))
{
if(l==-1 && u==-1)
break;
x=0;
y=0;
for( i=0; i<e; i++)
{
if(prime[i]>=l && prime[i]<=u )
{
x++;
if(prime[i]%4==1)
{
y++;
}
}
if(prime[i]>u)
break;
}
if(l<=2 && u>=2)
{
y++;
}
printf("%d %d %d %d\n",l, u, x, y );
}
return 0;
}
