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Daily Challenge #103 - Simple Symbols

Write a function that will take a string and determine if it is an acceptable sequence. The string will be composed of + and = symbols with several characters between them. For the string to be acceptable, each character must be surrounded by + symbols.

Examples:
(++d+===+c++==a) => false, because a is not surrounded by +.
(+d+e+===+q+=) => true, because all characters are surrounded by +.

Test cases:
"f++d+"
"++q++qq=z"
"==++z+=+q+"

Want to propose a challenge idea for a future post? Email yo+challenge@dev.to with your suggestions!

Top comments (15)

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jvanbruegge profile image
Jan van Brügge

simple Haskell solution:

verify :: String -> Bool
verify [] = True
verify ('+':x:'+':xs)
    | isLetter x = verify $ '+':xs
verify (x:xs)
    | isLetter x = False
    | otherwise = verify xs
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idanarye profile image
Idan Arye

I took your solution and simplified it:

verify :: String -> Bool
verify [] = True
verify ('+':x:'+':xs) = verify $ '+':xs
verify ('+':xs) = verify xs
verify ('=':xs) = verify xs
verify (_) = False

Also note that nothing in the question indicates the characters other than = and + can only be letters. Your version would accept 1 even though 1 is a character and it is not surrounded by +s.

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jvanbruegge profile image
Jan van Brügge

This solution assumes that the only other character is =. No idea if you can assume this

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idanarye profile image
Idan Arye

The string will be composed of + and = symbols with several characters between them.

If I'm reading this correctly, it means that the characters are categorized into three categories:

  1. +
  2. =
  3. Other

So any character other than + and = must be surrounded by +s - which is exactly what my version checks.

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aminnairi profile image
Amin • Edited on

Whoa, I was comming with something that involved using an indexedMap but your solution is very clever. Thanks for sharing your awesome answer!

Also, isn't isLetter part of Data.Char? Or no need to import that to use the isLetter function?

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jvanbruegge profile image
Jan van Brügge

yes, that function is from Data.Char, I omitted the import together with the module header.

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edreeseg profile image
Ed Reeseg • Edited on

I've never been the best with Regex, but here's a possible attempt:

JavaScript

const acceptableSequence = str => !/(?<!\+)\w|\w(?!\+)/.test(str);

EDIT: Misread the requirements, don't need to account for end and beginning of line characters as exceptions.

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edreeseg profile image
Ed Reeseg

That's a good point. I figured I'd use \w since nothing in the challenge indicated that the characters need be only alphabetical, but obviously you could just as easily sub in [a-zA-Z] or whatever fits the use case.

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erezwanderman profile image
erezwanderman

Javascript:

acceptable = str => [...str].every((x, i, a) => x == '+' || x == '=' || (a[i - 1] == '+' && a[i + 1] == '+'))
 
edreeseg profile image
Ed Reeseg

That definitely makes the most sense, given the examples. I really appreciate you reaching out to clarify - definitely want to make sure I'm accurately hitting objectives.

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