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PALPRIM - Palindromic Primes (Hard) |
A Palindromic number is a number without leading zeros that remains the same when its digits are reversed. For instance 5, 22, 12321, 101101 are Palindromic numbers where as 10, 34, 566, 123421 are not. A Prime number is a positive integer greater than 1 that has no positive divisors other than 1 and itself. For example, 2, 31, 97 are Prime numbers but 1, 10, 25, 119 are not. A Palindromic Prime number is both palindromic and prime at the same time. 2, 3, 131 are Palindromic Prime numbers but 6, 17, 3333 are not. Given a positive integer N, output the largest palindromic prime number not greater than N.
Input
The first line contains an integer T denoting the number of test cases. Each of the subsequent T lines contain a single integer N without leading/trailing spaces.
Output
Print T lines. For each test case, print a single integer denoting the largest palindromic prime number which does not exceed N.
Constraints
1 ≤ T ≤ 10^6
2 ≤ N ≤ 10^13
Example
Input: 3 2 10 666 Output: 2 7 383
Note Large input and output, please use faster I/O methods.
Added by: | sgtlaugh |
Date: | 2016-02-26 |
Time limit: | 15s |
Source limit: | 50000B |
Memory limit: | 1536MB |
Cluster: | Cube (Intel G860) |
Languages: | All except: ASM64 GOSU JS-MONKEY |
Resource: | Own Problem |
hide comments
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2021-07-08 05:52:19 [Lakshman]
@@sgtlaugh Can you please verify all submissions by CRV college? all seems to be the same. [NG]: sgtlaugh, please take log of users from that school who cheated on your problem again, I can see them doing it elsewhere too and will contact admins about this, thanks. -> Yes they are cheating. Looks like they're already banned here. Last edit: 2021-09-02 18:54:04 |
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2020-09-17 15:57:31
Strange. I took 12% off the run time of my big test file at home, yet it took longer than my first submission. (sgtlaugh): That's probably because the runtime of your codes can vary and depends a lot on the compiler, platform, architecture, etc. Last edit: 2020-11-06 22:27:18 |
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2016-10-03 13:04:11
@sgtlaugh : could you please give a test case where my submission number 17841013 gives TLE. (sgtlaugh): You are ignoring the fact that T can be as large as 10^6. Try giving the cases mentioned in the comments below 10^6 times and your code should time out. Last edit: 2019-02-28 22:38:44 |
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2016-03-03 18:16:32
Is T (number of trials) really as high as 1,000,000? Using what I thought was a fast palindrome generator and Miller Rabin primality test, it's still between 5-10 seconds per computation for random 13-digit numbers: working on 8572115172675 7499982899947 working on 5127997788693 3899960699983 working on 440780157081 99999199999 working on 6546887935149 3899960699983 ... @sgtlaugh: is a mathematical insight needing to be found? or can this all optimization be done algorithmically? (sgtlaugh): Yes the number of test cases can be as high as 1,000,000. A little mathematical insight and some observations are required but most of the optimization can be done algorithmically. Oh and your output is wrong for 8572115172675, 5127997788693 and 6546887935149. Last edit: 2016-03-04 13:52:10 |
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2016-03-01 09:39:35 [Lakshman]
@sgtlaugh can this be done without pre-computation? (sgtlaugh): This can be solved without hard coding a table of pre-computed values if that's what you mean. Last edit: 2016-03-01 15:14:52 |
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2016-02-27 18:12:58
Optimized my algorithm yet got tle help somebody (sgtlaugh): You cannot get Accepted with such a naive approach. can you please tell me what is my execution time? (sgtlaugh): 100 billion years Last edit: 2016-02-28 22:52:10 |
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2016-02-26 21:10:04
@Blue Mary,i am getting WA.Could u plz provide some more test cases so i can figure out my mistake?? |
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2016-02-26 15:28:42
@Blue.Mary any help on algorithm which part to improve please getting tle Last edit: 2016-02-26 15:31:22 |
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2016-02-26 12:39:50 [Rampage] Blue.Mary
@sgtlaugh, I've optimized my code a little, never mind :-) |
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2016-02-26 12:38:57 Scape
@Blue Mary, your first submission gets Accepted instead of TLE with C++ 5 |