[Community Puzzle] Format string validation

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#1

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#3

I’ve been lost on this for a bit. Maybe I’m taking the wrong approach?

I’m coding in JS, and I’ve had a few different logics I’ve tried out, and it end in one of two ways -
-The code becomes too complex to follow, so I paste my code into a notepad just in case, and start over.
-Limited by the approach

All of my logic seems to start the same. Divide the ‘format’ by “~”, and use String manipulation to find the portions of it within ‘text’. This typically works to start, and has been my initial approach.

My first logic worked for every test except the last. I think I know why.
In a situation where the text is ZZABXDABCDFFABYDZZ, and the format ~AB?D?F~
I was working through it, dividing it out by the "?"s after dividing it out by "~"s, and although it’d find an instance of “AB?” in the string, it didn’t find the right one, and I hadn’t programmed a way for it to backtrack and try the next.

My most recent logic was to separate into two parts. Firstly, the beginning and the end. Thinking if I could separate the special case of if it starts with “~” or not, from the rest of the logic, it might be easier.

I’m thinking maybe the answer lies somewhere in recursion? When learning programming, recursion is a topic that’s always given me trouble. I usually am able to understand enough to pass the courses, but never enough to apply it in actual programming. I feel like it’s a valuable tool, but I struggle when applying it.

TL;DR →
I would like help.
Hints, or tips for the puzzle, or learning recursion in a way that I can see how to apply it?
Javascript-specific resources would be nice on the recursion, but I’m also fine just learning the general logic of it.

#4

Most of the published Python solutions I can see use either regex or recursion, so recursion is definitely a way to go. There are also solutions using dynamic programming and other approaches, but they are very few.

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#5

If you’re not ready for recursion, you can solve this puzzle without it.

  • First, write an “equals” function, to accept the “?” character (so that “ABCD” and “AB?D” would return true).
  • Then, write a “find” function, using your “equals” function (so that it would find “AB?D” in “ZZABCDZZ”), returning the index.

With those tools, you can just separate words by “~” as you said, and find each word in the text. Be careful about starting each search at the end of the previous one (that’s why “find” returns an index. You start your search at the previous index + previous word.length(), so that “AB~BC” wouldn’t match in “ABC”).

And if it’s too easy with that 
 you can try recursion. :wink:

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#6

I’m always sad when I hear this because recursion is supposed to feel a lot more “natural” than programming with loops, so if a teacher makes loops easier than recursion they are doing something wrong in my opinion.

One way to think of recursion is that you have a trusted assistant who already knows how to do the task; you have to make just a little bit of progress yourself, but you can pass most of the task, as a subtask, to your assistant who already knows how to do it.

For instance, imagine you have to match ABXDABCDFF against ~AB?D?F~.

The very first thing to do is decide whether to include the first A into the ~ or not.

If you include it, then you’re left with matching BXDABCDFF against ~AB?D?F~, which you pass to your assistant.

If you don’t include it, then you’re left with matching ABXDABCDFF against AB?D?F~, which you pass to your assistant.

So this gives us the following recurrence relation:

match(“~AB?D?F~”, “ABXDABCDFF”) =
Ask your assistant to test match(“~AB?D?F~”, “BXDABCDFF”) and to test match(“AB?D?F~”, “ABXDABCDFF”), and use the result of these two subtasks to get the result of your task.

Now this is a recurrence relation, you can

  • use it directly to write a recursive function
  • use it to fill a dynamic programming table where M[i,j] stores the result of match(substring starting at index i, substring starting at index j)
  • use it for a stack-based or queue-based approach where you store all the pairs (format,text) that you want to try to match
  • or anything else of your choosing.

(Also note I arbitrarily decided to do remove characters from left to right, but you can also do it from right to left if you prefer, ie remove the F before the A)

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#7

ty all for the tips ~
I’m going to try again later today.

I’d really like to do it using recursion, so I’m going to try that first.
I’ll comment again once I triumphantly complete the puzzle >:^)

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#8

Thank you very much for this puzzle, I really enjoyed it.
It reminded me some lessons I had long time ago.

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#9

I DID IT!!! WITH RECURSION!!! (kinda)
I don’t know if it still counts as recursion, because I called the recursive function inside of a loop, but it works :slight_smile:

Best part is, would have worked on my first try, but I forgot to pass the previous value of a variable when taking a step back, so it was statically set to false instead of taking a step back and using the previous value.

TL;DR thx for everyone that helped :):):).

Edit:

I’m now realizing how much simpler this problem would have been to solve with regex xD

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#10

Bonjour, je ne comprends pas pourquoi le test 8 est considéré comme bon.

DĂ©but du texte = IboJSRam>|6&V17T_M|pww)m,<ns8{%9G5%%WT"S=f}kztLQ^eP-T/P-u@?LgbWjnmE
DĂ©but format . = Ibo~ . . . . >|6&~ . . . . . .pw~ )m~ . . . .{~ . . . . . . . . . . . . . . . . . . . -u@?LgbWjnm?/JB<
ça coince ici. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .^

puisque aprùs le tiret (-) le format montre un ‘u’ alors que le texte donne un ‘T’

Que n’ai-je pas compris dans les consignes ? Merci de m’éclairer.

Hello, I don’t understand why test 8 is considered good.

Start of text . .= IboJSRam>|6&V17T_M|pww)m,<ns8{%9G5%WT “ S=f}kztLQ^eP-T/P-u@?LgbWjnmE
Start format . = Ibo~ . . . . >|6&~ . . . . . .pw~ )m~ . . . {~ . . . . . . . . . . . . . . . . . . . .-u@?LgbWjnm?/JB<
it’s sticking here. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .^

since after the hyphen (-) the format shows a ‘u’ whereas the text shows a ‘T’.

What did I not understand in the instructions? Thanks for clarifying.

#11

You’re saying

Text:   { %9G5%%WT"S=f}k`ztLQ^eP -T/P -u@?LGbWjnmE/JB<c
          ~~~~~~~~~~~~~~~~~~~~~~  not matched from here
Format: { ~                      -u@?LGbWjnm?/JB<c

But you can also match the format this way:

Text:   { %9G5%%WT"S=f}k`ztLQ^eP -T/P -u@?LGbWjnmE/JB<c
          ~~~~~~~~~~~~~~~~~~~~~~ ~~~~
Format: { ~                           -u@?LGbWjnm?/JB<c
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#12

does someone know what is in test Big case, I passed all the tests except the one after submitting the code, I would like to know what is in this test.
Can someone help me please?

#13

In Validator 8 (Big case), the input text is the same as that of Test 8, while the input format is around 50% the same as that of Test 8.

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#14

you fail probably because ~?

#15

Merci pour cet Ă©claircissement.

Certaines consignes mĂ©riteraient d’ĂȘtre amĂ©liorĂ©es.

C’est notamment le cas pour le problùme “WAR”, la bataille navale, pour lequel j’ai vu passer une multitude de demande d’aide concernant le ramassage des cartes.

Ceci dit, j’aurais dĂ» me douter qu’il fallait comprendre les consignes diffĂ©remment puisque des participants de "format string validation’ avaient rĂ©solu ce problĂšme. Je rĂ©flĂ©chirai plus longtemps la prochaine fois :wink:

Thanks for the clarification.

Some of the instructions could be improved.

This is particularly the case for the “WAR” problem, the naval battle, for which I’ve seen a multitude of requests for help in collecting the cards.

Having said that, I should have known that the instructions needed to be understood differently, as participants in “format string validation” had solved this problem. I’ll think longer next time :wink:

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#16

I understand what you mean, but it doesn’t mean that it will match with the first “-”. Maybe there are more than one character in the text . That’s why you have to search till end of the text. As you can see at the second “-” it works.

#17

Hello there,

I think I bypassed the validators (maybe not well written enough) and then succeded to this puzzle illegitimately. Not willingly ; I just realized (after the full green tests + submit) that in some specific cases, my code would not work.
I just check for all substring in format.split(‘~’) if it is in the text (managing the ? joker character of course).
Then I wrote a customized test :
lol$lol$hello$hey
~$~$hello$
Found (with my code) : MATCH
Expected (according to my view) : FAIL
Problem comes when there are more than 2 same substrings in the text.
I have ideas for fixing my solution. But first, I would like to know what do you think about my thought.

I do not know if an admin can read my code, or if I can paste it here (sounds a wrong idea).

#18

I believe the answer to your custom test is indeed FAIL. And you’re absolutely right in thinking that you should avoid posting solution codes here.

1 Like