Title description
Because 151 is both a prime number and a palindrome number (from left to right and right to left are the same), 151 is a palindrome prime number.
Write a program to find all palindrome prime numbers in the range [a,b] (5≤a<b≤100,000,000) (100 million).
Input format
Line 1: Two integers a and b.
Output format
Output a list of palindrome prime numbers, one per line.
Sample input and output
| Enter #1 | Output #1 |
|---|---|
| 5 500 | 5 |
| 7 | |
| 11 | |
| 101 | |
| 131 | |
| 151 | |
| 181 | |
| 191 | |
| 313 | |
| 353 | |
| 373 | |
| 383 |
Idea: The input interval may be very large. According to the conventional enumeration, T will be dropped. Therefore, this question directly constructs a palindrome string, and then judges whether it is a prime number (the mantissa of the number must not be an odd number, and the mantissa is determined The loop += 2 can reduce some unnecessary loops), then you can ac this question.
code show as below:
#include <iostream>
#include <cmath>
using namespace std;
int judge(int x)
{
int i;
if(x==1)
return 0;
for(i=2;i<=sqrt(x);i++)
{
if(x%i==0)
return 0;
}
return 1;
}
int main()
{
int d1,d2,d3,d4,d5,shu,l,r;
cin>>l>>r;
if(l<=10)
for(d1=1;d1<=9;d1++)
{
shu=d1;
if(shu>r)
break;
if(shu<l)
continue;
if(judge(shu))
cout<<shu<<endl;
}
if(l<=100)
for(d1=1;d1<=9;d1+=2)
{
shu=d1*10+d1;
if(shu>r)
break;
if(shu<l)
continue;
if(judge(shu))
cout<<shu<<endl;
}
if(l<=1000)
for(d1=1;d1<=9;d1+=2)
{
for(d2=0;d2<=9;d2++)
{
shu=d1*100+d2*10+d1;
if(shu>r)
break;
if(shu<l)
continue;
if(judge(shu))
cout<<shu<<endl;
}
}
if(l<=10000)
for(d1=1;d1<=9;d1+=2)
{
for(d2=0;d2<=9;d2++)
{
shu=d1*1000+d2*100+d2*10+d1;
if(shu>r)
break;
if(shu<l)
continue;
if(judge(shu))
cout<<shu<<endl;
}
}
if(l<=100000)
for(d1=1;d1<=9;d1+=2)
{
for(d2=0;d2<=9;d2++)
{
for(d3=0;d3<=9;d3++)
{
shu=d1*10000+d2*1000+d3*100+d2*10+d1;
if(shu>r)
break;
if(shu<l)
continue;
if(judge(shu))
cout<<shu<<endl;
}
}
}
if(l<=1000000)
for(d1=1;d1<=9;d1+=2)
{
for(d2=0;d2<=9;d2++)
{
for(d3=0;d3<=9;d3++)
{
shu=d1*100000+d2*10000+d3*1000+d3*100+d2*10+d1;
if(shu>r)
break;
if(shu<l)
continue;
if(judge(shu))
cout<<shu<<endl;
}
}
}
if(l<=10000000)
for(d1=1;d1<=9;d1+=2)
{
for(d2=0;d2<=9;d2++)
{
for(d3=0;d3<=9;d3++)
{
for(d4=0;d4<=9;d4++)
{
shu=d1*1000000+d2*100000+d3*10000+d4*1000+d3*100+d2*10+d1;
if(shu>r)
break;
if(shu<l)
continue;
if(judge(shu))
cout<<shu<<endl;
}
}
}
}
if(l<=100000000)
for(d1=1;d1<=9;d1+=2)
{
for(d2=0;d2<=9;d2++)
{
for(d3=0;d3<=9;d3++)
{
for(d4=0;d4<=9;d4++)
{
shu=d1*10000000+d2*1000000+d3*100000+d4*10000+d4*1000+d3*100+d2*10+d1;
if(shu>r)
break;
if(shu<l)
continue;
if(judge(shu))
cout<<shu<<endl;
}
}
}
}
return 0;
}