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

int prime_test( long x )
{
long sqx = (long)sqrt( x ) , t;
for( t = 3; t <= sqx ; t += 2 )
if( x % t == 0 )
return 0;
return 1;
}

int slove( long x , long * r )
{
long a = x / 10;

while( a > 10 )
{
x *= 10;
x += a % 10;
a /= 10;
}

if( a%2 == 0 || a == 5 )
return 0;

x = x * 10 + a;
if( prime_test( x ) )
return *r = x , 1;
return 0;
}

int main()
{
long i , r;
printf( "2\n3\n5\n7\n" );

for( i = 10; i < 100; ++i )
{
if( slove( i , &r ) )
printf( "%d\n" , r );
}

for( i = 100; i < 1000; ++i )
{
if( slove( i , &r ) )
printf( "%d\n" , r );
}

for( i = 1000; i < 10000; ++i )
{
if( slove( i , &r ) )
printf( "%d\n" , r );
}

for( i = 10000; i < 100000; ++i )
{
if( slove( i , &r ) )
printf( "%d\n" , r );
}

return 0;
}


以上为我的代码 希望大侠们能把它改成求任意范围内回文素数的程序。。。。。

沙发  高手快来帮忙啊

没太明白你的意思  ？  十亿已经很大了

刚刚学习了不长时间 问题不少啊  这个我已经想了两天了  改了几次  没成  主要是要把时间限制在十秒以内

还在么  请您指教

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

int main()
{
    long int t,a,b; //定义最后输出的结果t、筛选范围等
    int i,j,k,l,m,n,x,flag = 1,d[3]; //定义筛选回文素数所需的计数器、100内回文素数数组等
    scanf("%ld%ld", &a,&b); //将输入的两个整数按顺序作为输出结果的下限、上限
    d[0] = 5; //由于100内回文素数非常少，因此直接将它们定义到数组中以减少代码量与运算量
    d[1] = 7;
    d[2] = 11;
    for (i = 0; i < 3; i++) //对100内回文素数是否符合所给的范围进行判定
        {
            if ((a <= d[i]) && (d[i] <= b)) printf("%d\n",d[i]);
        }
    for (i = 1; i <= 9; i++) //筛选出三位回文素数并对是否符合所给的范围进行判定
    for (j = 0; j <= 9; j++)
       {
        flag = 1;
        t = i*101 + j*10;
        n = sqrt(t);

        for (x = 2; x <= n && flag; x++)

        {
            if(t%x == 0) flag = 0;
        }

        if(t < a || t > b) flag = 0;

        if(flag)
        printf("%ld\n", t);
       }
    for (i=1; i <= 9; i++) //筛选出五位回文素数并对是否符合所给的范围进行判定
    for (j=0; j <= 9; j++)
    for (k=0; k <= 9; k++)
        {
        flag = 1;
        t = i*10001 + j*1010 + k*100;
        n = sqrt(t);

        for (x = 2; x <= n && flag; x++)

        {
            if(t%x == 0) flag = 0;
        }

        if(t < a || t > b) flag = 0;

        if(flag)
        printf("%ld\n", t);
        }
    for (i = 1; i <=9 ; i++) //筛选出七位回文素数并对是否符合所给的范围进行判定
    for (j = 0; j <=9 ; j++)
    for (k = 0; k <=9 ; k++)
    for (l = 0; l <= 9; l++)
        {
        flag = 1;
        t = i*1000001 + j*100010 + k*10100 + l*1000;
        n = sqrt(t);

        for (x = 2; x <= n && flag; x++)

        {
            if(t%x == 0) flag = 0;
        }

        if(t < a || t > b) flag = 0;

        if(flag)
        printf("%ld\n", t);
        }
    for (i = 1; i <= 9; i++) //筛选出九位回文素数并对是否符合所给的范围进行判定
    for (j = 0; j <= 9; j++)
    for (k = 0; k <= 9; k++)
    for (l = 0; l <= 9; l++)
    for (m = 0; m <= 9; m++)
        {
        flag = 1;
        t = i*100000001 + j*10000010 + k*1000100 + l*101000 + m*10000;
        n = sqrt(t);

        for (x = 2; x <= n && flag; x++)

        {
            if(t%x == 0) flag = 0;
        }

        if(t < a || t > b) flag = 0;

        if(flag)
        printf("%ld\n",t);
        }
        return (0);
}