素数问题

http://poj.org/problem?id=2689

筛选素数 先建一个小素数表 2-sqrt（max) 再根据这个表来进行区间素数的筛选

#include<math.h>
#include<stdio.h>
#include<string.h>
__int64 x[1000011];
int pr[46500],pd[46500],pg[1000011];
int main()
{
    __int64  n,m,x1,x2,x3,x4,y;
    int i,j,k;
    for(i = 2 ; i <= 46500 ; i++)
    {
        if(!pr[i])
        {
            for(j = i+i ; j <= 46500 ; j+=i)
            if(pr[j])
            pr[j] = 1;
        }
    }
    int g = 0;
    for(i = 2 ; i <= 46500 ; i++)
    if(!pr[i])
    pd[g++] = i;
    while(scanf("%I64d%I64d",&n,&m)!=EOF)
    {
        memset(pg,0,sizeof(pg));
        k = 0;
        for(i = 0 ;i < g ; i++)
        {
            if(n%pd[i])
            y = n/pd[i]+1;
            else
            y = n/pd[i];
            if(n<=pd[i])
            y++;
            for(j = y*pd[i]-n ; j <= m-n ; j+=pd[i])
            if(!pg[j])
                pg[j] = 1;
        }
        if(n==1)
            pg[0] = 1;
        k = 0;
        for(i = 0 ; i <= m-n ; i++)
        if(!pg[i])
        {
            x[k++] = i+n;
        }
        if(k>1)
        {
            __int64 min = x[1]-x[0],max=0;
            x3 = x[0];
            x4 = x[1];
            for(i = 1 ;i <k ; i++)
            {
                if(x[i]-x[i-1]>max)
                {
                    max = x[i]-x[i-1];
                    x2 = x[i];
                    x1 = x[i-1];
                }
                if(x[i]-x[i-1]<min)
                {
                    min = x[i]-x[i-1];
                    x4 = x[i];
                    x3 = x[i-1];
                }
            }
            printf("%I64d,%I64d are closest, %I64d,%I64d are most distant.\n",x3,x4,x1,x2);
        }
        else
        printf("There are no adjacent primes.\n");
    }
    return 0;
}