1.5.2 Prime Palindromes

The number 151 is a prime palindrome because it is both a prime number and a palindrome (it is the same number when read forward as backward). Write a program that finds all prime palindromes in the range of two supplied numbers a and b (5 <= a < b <= 100,000,000); both a and b are considered to be within the range .

PROGRAM NAME: pprime

INPUT FORMAT

Line 1:

Two integers, a and b

SAMPLE INPUT (file pprime.in)

5 500

OUTPUT FORMAT

The list of palindromic primes in numerical order, one per line.

SAMPLE OUTPUT (file pprime.out)

5

7

11

101

131

151

181

191

313

353

373

383

 

代码：

#include <iostream>
#include <cstdio>
#include <algorithm>
#define ll long long
using namespace std;
char s[10];
int l;
bool p(ll x)
{
    if(x==1) return false;
    if(x==2) return true;
    for(ll i=2;i*i<=x;i++){
        if(x%i==0) return false;
    }
    return true;
}

int main()
{
    freopen("pprime.in","r",stdin);
    freopen("pprime.out","w",stdout);
    ll a,b,c,d,e,x,y,m;
    scanf("%lld %lld",&x,&y);
    for(a=1;a<=9;a++){
        if(p(a)&&a>=x&&a<=y) cout<<a<<endl;
    }
    for(a=1;a<=9;a+=2){
        m=11*a;
        if(p(m)&&m>=x&&m<=y) cout<<m<<endl;
    }
    for(a=1;a<=9;a+=2){
        for(b=0;b<=9;b++){
            m=101*a+10*b;
            if(p(m)&&m>=x&&m<=y) cout<<m<<endl;
        }
    }
    for(a=1;a<=9;a+=2){
        for(b=0;b<=9;b++){
            for(c=0;c<=9;c++){
                m=10001*a+1010*b+100*c;
                if(p(m)&&m>=x&&m<=y) cout<<m<<endl;
            }
        }
    }
    for(a=1;a<=9;a+=2){
        for(b=0;b<=9;b++){
            for(c=0;c<=9;c++){
                for(d=0;d<=9;d++){
                    m=1000001*a+100010*b+10100*c+1000*d;
                if(p(m)&&m>=x&&m<=y) cout<<m<<endl;
                }
            }
        }
    }
    return 0;
}