PRPALIN - Editorial

editorial
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1

PROBLEM LINK:

Practice

Author: ADMIN

Editorialist: SUSHANT AGARWAL

DIFFICULTY:

SIMPLE

PREREQUISITES:

Basic looping,Conditional statements

PROBLEM:

You will be given an integer N, 1 ≤ N ≤ 1000000. You must find
the smallest integer M ≥ N such that M is a prime number and M is a
palindrome.

EXPLANATION:

Check every odd number after N (using a loop) for 2 properties

1)It should be prime 2) The number should be equal to its reverse.

Print the first number that satisfies these 2 properties and then break out of the loop when this number is encountered.

EDITORIALIST’S SOLUTION:

Editorialist’s solution can be found here.

1 Like
2

Nice job, but please format your code if you want someone to be able to understand it easily - use for example this - http://prettyprinter.de/index.php

…after N…

is not correct, M >= N right?

1 Like
3

#include<stdio.h>
#include<math.h>
int check(int num)
{
int rev_num = 0;
while(num > 0)
{
rev_num = rev_num*10 + num%10;
num = num/10;
}
return rev_num;
}
int main()
{
int n,i;
scanf("%d",&n);
if(n==1)
{
printf(“2\n”);
}
else if(n==2)
printf(“3\n”);
else{
if(n%2==0)
n++;
else
n=n+2;
do{
int x=sqrt(n);
for(i=3;i<=x;i++)
{
if(n%i==0)
break;
}
if(n%i!=0)
{ int j=check(n);
if(j==n)
{ printf("%d\n",n);
break;
}
}
n=n+2;
}while(1);
}
return 0;
}
why this not work

4

Please ask questions in Discuss -> Forums -> Ask a Question.

Do not post questions like this as an answer.

5

The solution given in this editorial is wrong. For the input of 10010 it gives output 10201 but rather it should be 10301

6

answer is right…10201 is smaller than 10301

7

why my solution is going for tle,…
http://www.codechef.com/viewsolution/6782096

8

10201 is divisible by 101
hence it is not a prime no
Hence the awnser for 10010 is 10301

9

10201 is divisible by 101
hence it is not a prime no
Hence the answer for 10010 is 10301

10

sir i have applied seive of atkins to found prime but still getting tle

11

have u submitted it or checking it in codechef IDE?

12

Serious issue - Editorialist’s solution is wrong as output for 10000 is 10201 which is 101^2.
This also means that the testcases are weak.