World’s longest palindrome? | Hacker News Reader

World’s longest palindrome?

pinchofintelligence.com

58 pointsrmeertens57 comments

"A man, a plan, a canoe, pasta, heros, rajahs, a coloratura, maps, snipe, percale, macaroni, a gag, a banana bag, a tan, a tag, a banana bag again (or a camel), a crepe, pins, Spam, a rut, a Rolo, cash, a jar, sore hats, a peon, a canal-- Panama!" - Guy Steele, CLTL2

Some years after the faked death of John Darwin, who disappeared after rowing out to sea in his canoe, and was planning to start a new life with his wife in Panama with the insurance payout, the Grauniad had the headline "A man. A plan. A canoe. Panama" in an article (https://www.theguardian.com/uk/2008/jul/23/canoe.ukcrime1) about the case.

He could have at least had the good decency to have used a KayaK.

Pretty sure it was a kayak. People in the UK are very confused by the difference. E.g. British Canoe Union largely supports kayaking. I tend to use the terms interchangeably having been an active kayaker for around 25 years. The British public really struggle with the difference.

See banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, banana, bees.

For any N "See [banana,]* bees." can be longer than N.

"Dammit, I'm mad..." https://quotereference.wordpress.com/2014/12/11/dammit-im-ma...

PS I converted this into three palindromic tweets https://twitter.com/sep332/status/928484353310711808

How does this count as a palindrome? It's just a bunch of nonsense words (ignoring all the acronyms, are the rest all actually even really words?) separated by commas, that doesn't even seem to pretend to take on the structure of a sentence.

Am I misunderstanding the level of coherence of the text? If the requirements are that loose, it seems it would be trivial to generate a 'palindrome' of arbitrary length.

Think of it like an ad slogan.

"A man, a plan, a canal-- [you should book a trip to] Panama[, a country whose history is summed up by this witty list of things]!"

What I'd like to see is a version where instead of optimizing just for length, the palindrome is optimized for noun-phrases that genuinely have legit connections to Panama (as the brilliant original, "a plan, a man, a canal", does).

Apologies, I was actually referring to the very large (6MB!) palindrome text file [0] provided if you follow the article link to the GitHub project [1]. I guess the palindrome of discussion in this link is somewhat ambiguous, because there's not one specific palindrome that the article refers to.

[0] https://raw.githubusercontent.com/rmeertens/palindromes/mast... [1] https://github.com/rmeertens/palindromes

It's the same thing. "A man, a plan, (6MB worth of other junk)-- Panama!"

It's questionable what that other junk has to do with Panama. But grammatically, the structure is the same.

I was recently dumbfounded by the fact that

    ()()

is not a palindrome, but

    ())(

is. It's obvious, sure, but it still doesn't look right.

It's not obvious for me (maybe you are joking and I didn't get it)

Try substituting other symbols, which makes it easier to see. 1 for ( and 0 for ) for example.

Then we have

and

mindblow

It depends on your definition of palindrome. Is it 'reads the same forwards or backwards' or is it 'had the same characters in the second half as in the first, but in reverse order'?

You'll find that according to most dictionaries, ()() is the palindrome here.

Unless you're a robot.

Try replacing ( with a and ) with b : abab -> not palindrome abba -> palindrome

For a second I thought you have the most fitting username ever for this discussion, but then I saw that your account has just been created :D

or substitute the parans to a and b

()() --> abab

())( --> abba

)(() --> baab

We coders could get fooled by this question if we dont pay much attention

The longest palindrome has infinite length. Start with any palindrome, e.g. "radar". You can make a new palindrome: "radar, sides reversed, is radar". That can then be used to create the palindrome "radar, sides reversed, is radar, sides reversed, is radar, sides reversed, is radar".

You can repeat this indefinitely.

"Never odd or even" is one some here might like to see, and perhaps suggests the shorter palindrome, "NaN".

World's shortest palindrome:

There's a link which takes you to the list of palindrome dates mentioned on the website [1]. There's 38 of them, but they all take the MM/DD/YYYY format into consideration. I wonder how much of a difference it would be by taking DD/MM/YYYY instead.

[1] https://www.livescience.com/33583-palindrome-dates-21st-cent...

Or YYYY-MM-DD as a few of us obsessive smallendians keep insisting.

Heh, they'd just be the reverse of DD-MM-YYYY :)

But yes, YYYY-MM-DD all the way. It's indispensable to me when sorting file names by date.

Different word trivia that I find fascinating that I feel HNers will also appreciate:

(twelve plus one) is an anagram of (eleven plus two)

I guess that should be called a mathagram?

I was a fan of this palindromic short story (also in honor of the year 2002): http://spinelessbooks.com/2002/palindrome/

Here's a handcrafted one in Polish, 33K+ characters: http://www.palindromy.pl/pal_naj.php

I'm also reminded of this IOCCC entry: https://www.ioccc.org/1987/westley/westley.c. Strictly speaking, it's not composed of palindromes because of the mirror-image brackets and slashes, but still, impressive.

I have to point out Weird Al's "Bob": https://www.youtube.com/watch?v=JUQDzj6R3p4

It's not a palindrome, but is a semi-sensical song masterfully composed entirely out of palindromes (which also does a great job poking fun at Bob Dylan).

This one is a valid sentence in Dutch:

"Nelli plaatst op n parterretrap n pot staalpillen."

The 'n's are a bit of an issue though, 'n in dutch means 'een', but reversed that doesn't work so the 'e's got dropped and replaced by "'" but they move from one side of the n's to the other in the reversal.

We used find the longest palindrome in a string as an interview question at Amazon back in 2004

Did you require a certain time complexity? I came across this on Leetcode. I found it really trivial to implement the “test all substrings” algorithm, but fiendishly difficult to implement the “expand around centers” algorithm.

That's why trick puzzle questions are bad interview questions. Some people have read the centers algorithm

It’s not a trick question. It’s just writing a loop any CS graduate or equivalent autodidact should have absolutely no problem with.

We didn’t require any specific time or space complexity. If the candidate whipped out a suboptimal solution quickly and correctly and time permitted we might ask them about that though and how it might be improved. The purpose of the question is not to see if the candidate has memorized the answer or sees a trick, it’s so they can demonstrate basic proficiency and systematic reasoning.

Hug of death?

https://web.archive.org/web/20180809171552/http://www.pincho...

Thank you. Don't know why I'm being downvoted for asking.

perhaps someone took it too literal and thought, htaed fo guh != hug of death

I upvoted your comment to make it up for you...hope you have a good one...

Georges Perec in 1969: http://homepage.urbanet.ch/cruci.com/lexique/palindrome.htm (1247 words)

Perec also wrote a book with no letter E, a mystery about the missing letter. The English translation is called _A Void_. It's hard to make sense in parts, largely works.

At parts it discusses the mysterious missing letter (E is not know) like threeve, the integer between 3 and 4.

8102018 is not a palindromic because it isn't a valid format date (it is, but is nonsense, so not valid on my standards :).

examples of valid date formats are: yyyy-mm-dd dd-mm-yyyy

engage le jeu que je le gagne

For single words, in Dutch there is:

koortsmeetsysteemstrook

And Finnish has saippuakivikauppias.

Go hang a salami, I'm a lasagna hog.

So many dynamos

I thought the point of palindromes were that they

1: Are the same forwards and backwards

2: Make coherent sense

Still pretty cool nonetheless, I suppose

This palindrome is surprisingly disappointing. Almost every word appears 100s of times...

My 2 "go to" palindromes...

I know a fat man called Ella C Namtafawnoki.

I got hang of fog nah togi.

My two go to palindromes are Mr Merasemordnilapotogowtym!

Whats with Sadick? (15 times!). Also the F*, C and S words!

For a line level palindrome homage to Douglas Hofstadter's Crab Canon see

https://juliagalef.com/2017/02/21/a-poem-for-douglas-hofstad...

wo nemo toss a lasso to me now!

Rotavator

Ada

Yo banana boy

Racecar

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