usaco 1.5 sprime...枚举...

/*
    ID:chenjiong
    PROG:sprime
    LANG:C++
*/

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

int N;
int ans;

bool is_prime(int x)
{
    if ( x == 1 )
        return false;
    if ( x == 2 || x == 3 )
        return true;
    if ( x % 2 == 0 )
        return false;
    int i;
    for ( i = 3; i <= sqrt(x); i += 2)
        if ( x % i == 0 )
            return false;
    return true;
}

void dfs(int cur)
{
    if ( cur == N )
    {
        printf("%d\n",ans);
        return;
    }
    int i;
    if ( cur == 0 )
    {
        for ( i = 1; i <= 9; i++)
        {
            int tmp = ans;
            ans = ans * 10 + i;
            if ( is_prime(ans) )
            dfs(cur + 1);
            ans = tmp;
        }
    }
    else
    {
        for ( i = 1; i <= 9; i += 2)
        {
            int tmp = ans;
            ans = ans * 10 + i;
            if ( is_prime(ans) )
                dfs(cur + 1);
            ans = tmp;
        }
    }
}

int main()
{
    freopen("sprime.in","r",stdin);
    freopen("sprime.out","w",stdout);

    scanf("%d",&N);

    ans = 0;
    dfs(0);

    return 0;
}