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Posted on Oct 31, 2019

Daily Challenge #103 - Simple Symbols

#challenge

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 (10)

Jan van Brügge • Oct 31 '19

simple Haskell solution:

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

Idan Arye • Oct 31 '19

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.

Jan van Brügge • Nov 1 '19

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

Idan Arye • Nov 1 '19

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:

+
=
Other

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

Amin • Oct 31 '19 • Edited

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?

Jan van Brügge • Oct 31 '19

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

Ed Reeseg • Oct 31 '19 • Edited

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.

Ed Reeseg • Oct 31 '19

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.

erezwanderman • Oct 31 '19

Javascript:

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

Ed Reeseg • Nov 1 '19

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.