10235 - Simply Emirp

[JWizard]

Alright:

output for 1:

1 is not prime.

output for 2:

2 is prime.

output for 13:

13 is emirp.

thanks a lot for your help

[10153EN]

Same as mine except the one for input 1 (mine is prime, but it doesn't matter, as it's not an input, which is stated 1 < N < 1000000).

If you don't mind, could you send your codes through Private Message so that I can have a look at it? I am now very curious and it's interesting to me~

[10153EN]

I have received your codes~

I have not taken a in-depth look at it, but I just have done an interesting thing: I use a program to generate a file consisting of 2,3,4,5,...,999999, then use this file as the input file of my program and your program. Finally, I diff the output file generated by the two program and found that..... NO DIFFERENCE (at least found by the diff program in UNIX)

I can be sure that your program is of no problem~
Or something not releted to the problem introduces the WA~ e.g. submitted with wrong problem number? Haha.....

[JWizard]

I just checked and I had submitted with the right problem number .....
just resubmitted it and it works now
Thanks for your help

[deddy one]

I'm a bit confused about emirp ,can anyone define emirp more
clearly???

why 2 is not emirp ?????

thx in advance.

[kmhasan]

I quote from the problem statement:

An Emirp (Prime spelt backwards) is a Prime that gives you a different Prime when its digits are reversed

2 is not different than 2 when reversed...

[deddy one]

thx kmhasan, that clears up the whole thing now

[sohel]

if anyone can tell me why
this program is wrong
.... I would be very grateful.

#include<stdio.h>
#include<math.h>
int chkprime(unsigned long);

int main()
{
int k=0,cnt=0,j,in;
unsigned long n,rf=0,xf,fnum[50],num;
while(scanf("%lu",&n)!=EOF)
{
num=n;
if(!(n%2) || !(n%3)) {k=0;if(n==2 || n==3) k=1;}
else k=chkprime(n);
if(k==0) {printf("%lu is not prime.\n",num);continue;}
while(n!=0)
{ xf=n%10;
fnum[cnt]=xf;
n=n/10;
cnt++;
}
for(j=cnt-1,in=0;j>=0;j--,in++)
rf=rf+fnum[j]*pow(10,in);
if(!(rf%2) || !(rf%3)) {k=0;if(rf==2 || rf==3) k=1;}
else k=chkprime(rf);
if(k==0 ||(num==rf)) printf("%lu is prime.\n",num);
else printf("%lu is emirp.\n",num);
cnt=0;
k=0;
rf=0;
}
return 0;
}
int chkprime(unsigned long n)
{
unsigned long d;

unsigned long i,in,p=n-1;
d=1;
if(p==1) i=1;
for(in=4;in<=2147483648;in=in*2)
if(p<in) {i=in/2;break;}
for(;i>=1;i=i/2)

{
d=((d*d)%n);
if(p&i)
d=((d*2)%n);
}
if(d!=1) return 0;
if(n==3) return 1;
else if(n==5) return 1;
for(p=3;p<=sqrt(n);p+=2)
if(!(n%p)) return 0;
return 1;

}

[Red Scorpion]

Try This Test Case :
Note : that 2 is not emirp, but prime!

Sample input:
2
1
10
11
71
9001
10009901
1321
1099933

Sample Output
2 is prime.
1 is prime.
10 is not prime.
11 is prime.
71 is emirp.
9001 is emirp.
10009901 is not prime.
1321 is emirp
1099933 is emirp.

Hope this Helps.
GOOD LUCK
RED SCORPION

[bery olivier]

An Emirp (Prime spelt backwards) is a Prime that gives you a different Prime when its digits are reversed.

You should check if the mirror is different before the second prime test.

[saiqbal]

logical error i guess. modify the following code:
code to modify:
[cpp]if(isPrime(b))
if(a!=b)
printf("%lld is emirp.\n",a);
else
printf("%lld is prime.\n",a);
[/cpp]
code to replace with:
[cpp]if(isPrime(b)) {
if(a!=b)
printf("%lld is emirp.\n",a);
else
printf("%lld is prime.\n",a);
}
else
printf("%lld is prime.\n",a);
[/cpp]
and i think you should use long instead of long long.

good luck
-sohel

[lendlice]

anyone can help me
[cpp]//10235
#include<stdio.h>
#include<string.h>
main()
{
unsigned long n=0,tr1=0,tr2=0,in1=0,in2=0,i=0,j=0,num=2;
char in[100000];
while(scanf("%s",in)==1)
{
n=strlen(in);
j=n-1;
while(i<n)
{
in1=(in-'0')+in1*10;
in2=(in[j]-'0')+in2*10;
i++;
j--;
}
while(tr1==0&&num<in1)
{
if(in1%num==0)
tr1=1;
else
num++;
}
num=2;
if(in1==in2)
tr2=1;
while(tr2==0&&num<in2)
{
if(in2%num==0)
tr2=1;
else
num++;
}
if(tr1==1)
printf("%ld is not prime.\n",in1);
else if(tr1==0&&tr2==1)
printf("%ld is prime.\n",in1);
else if(tr1==0&&tr2==0)
printf("%ld is emirp.\n",in1);
tr1=0;
tr2=0;
in1=0;
in2=0;
num=2;
i=0;
}
}[/cpp]

[Sebasti]

Hi,

Change the limits of your while loops to sqrt(in1)+1 and sqrt(in2)+1.

If the TLE still, try precalc the prime numbers and put them on a big array
(sieve of eratostenes).

Bye.

[hank]

Try This Test Case :
Note : that 2 is not emirp, but prime!

Sample input:
2
1
10
11
71
9001
10009901
1321
1099933

Sample Output
2 is prime.
1 is prime.
10 is not prime.
11 is prime.
71 is emirp.
9001 is emirp.
10009901 is not prime.
1321 is emirp
1099933 is emirp.

Hope this Helps.
GOOD LUCK
RED SCORPION

1 is not prime!!

[saiqbal]

1 is not prime!!

it doesn't matter actually. problem statement says:

Assume that 1< N< 1000000.

so, 1 is not in the judge input

good luck
-sohel