Friday, February 18, 2011

10852 - Less Prime


#include <stdio.h>
#include <math.h>

#define M 10005
#define MH M/2
char prm[M/16+10];

void seive();
int isPrime(int);

int main()
{
    register int t,i,k,n;
    //freopen("in.txt","r",stdin);
    scanf("%d",&t);
   
    seive();

    while(t--)
    {
        scanf("%d",&n);
        k=n/2+1;

        for(i=k;k<=n;i++)
            if(isPrime(i))
            {
                printf("%d\n",i);
                break;
            }
    }
    return 0;
}


void seive()
{
    int lim = (int)sqrt(M),i,j;
    for ( i = 3; i <= lim; i += 2){
        if ( !(prm[i>>4]&(1<<((i>>1)&0x7))) )
        {
            for (j = i*i/2; j <= MH; j+=i) prm[j>>3] |= (1<<(j&0x7));
        }
    }
}

int isPrime(int n)
{
    if ( n < 2) return 0;
    if ( n == 2) return 1;
    if ( n%2 == 0) return 0;
    if ( !(prm[n>>4]&(1<<( (n>>1)&0x7))) ) return 1;
    return 0;
}

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