Exercise: Palindromes and Isograms

[btiffin]

Update to the REBOL version. I was so excited about getting a chance to use alter that I skipped the obvious, and I added tabs to the delimters this time. alter is short for alternate, it scans a series! and either inserts or removes the value. Its use is normally limited to handling flags, so I thought this would be another use, but unique is more appropriate.

REBOL:

#!rebol -c rebol [] line: ask "? " words: parse/all line " ^-" probe words foreach word words [     mod: uppercase trim/all copy word     if equal? mod reverse copy mod [print ["Palindrome:" word]]     if equal? length? unique mod length? mod [print ["Isogram:" word]] ]

wtd; Your exercises are cutting into my breaks!

[Saad]

rizzix wrote:

Saad Shouldn't you account for single-quoted strings?

Correct again. However I realised a better way of doing it with help from regular expressions

Was done with GHC version 6.8.2

Compiled via

code:

ghc <name> -package regex-compat-0.71.0.1

Haskell:

import List (sort, group) import Char (toLower, isAlpha) import Text.Regex main = getLine >>= \input -> mapM_ putStrLn $ filter (\word -> isPalindrome word || isIsograph word) $ separateWords [] $ fixString input     where         fixString string = subRegex (mkRegex "( *\\\\*(\'|\") *)") string "~"                 separateWords :: [String] -> String -> [String]         separateWords allWords "" = allWords         separateWords allWords (' ':rest) = separateWords allWords rest         separateWords allWords ('~':rest) = let (word, _:remainder) = span (\char -> char /= '~') rest in separateWords (allWords ++ [word]) remainder         separateWords allWords string = let (word, remainder) = span (\char -> char /= ' ' && char /= '~') string in separateWords (allWords ++ [word]) remainder                 isPalindrome :: String -> Bool         isPalindrome string = let word = map toLower $ filter isAlpha string in word == reverse word         isIsograph :: String -> Bool         isIsograph string = all (\letters -> length letters == 1) $ group $ sort $ map toLower $ filter isAlpha string

Basically I replace all the quotation types with a ~ and then its simple string manipulation

[rizzix]

what if the word was 'abc ~ def'

[Saad]

rizzix @ Sat May 10, 2008 2:10 pm wrote:

what if the word was 'abc ~ def'

It was done assuming that the words entered would be valid words.

However another version based on the same idea but with support of characters like ~ (although wtd could make what he wants more clear if he wants that kind of support or not)

Haskell:

import List (sort, group) import Char (toLower, isAlpha) main = getLine >>= \input -> mapM_ putStrLn $ filter (\word -> isPalindrome word || isIsograph word) $ separate input     where         separate :: String -> [String]         separate line = separateWords [] line             where                 separateWords :: [String] -> String -> [String]                 separateWords allWords "" = allWords                 separateWords allWords (' ':rest) = separateWords allWords rest                                     separateWords allWords ('\\':'\'':rest) = let (word, _:_:remainder) = span (\char -> char /= '\\') rest in separateWords (allWords ++ [word]) remainder                 separateWords allWords ('\\':'\"':rest) = let (word, _:_:remainder) = span (\char -> char /= '\\') rest in separateWords (allWords ++ [word]) remainder                 separateWords allWords ('\'':rest) = let (word, _:remainder) = span (\char -> char /= '\'') rest in separateWords (allWords ++ [word]) remainder                 separateWords allWords ('\"':rest) = let (word, _:remainder) = span (\char -> char /= '\"') rest in separateWords (allWords ++ [word]) remainder                 separateWords allWords string = let (word, remainder) = span (\char -> char /= ' ') string in separateWords (allWords ++ [word]) remainder                         isPalindrome :: String -> Bool         isPalindrome string = let word = map toLower $ filter (\x -> x /= ' ') string in word == reverse word             isIsograph :: String -> Bool         isIsograph string = all (\letters -> length letters == 1) $ group $ sort $ map toLower string

[rizzix]

Here's another approach to this, using Parser Combinators.

Scala:

import scala.util.parsing.combinator.lexical._; import scala.util.parsing.input.CharArrayReader.EofCh object Test extends Application {     case class Word(str : String)         def isIsoPalin(s : List[Char]) =  s == s.reverse || s.removeDuplicates == s         object Lexer extends Lexical {         type Token = Word                 val sq = '\''; val dq = '"'; val bs = '\\'                 def whitespace = ' '?                 def token = (             sq ~ ((bs ~ sq | chrExcept(sq, EofCh))+) ~ sq ^^ {case _ ~ xs ~ _ => Word(deflate(xs))}           | dq ~ ((bs ~ dq | chrExcept(dq, EofCh))+) ~ dq ^^ {case _ ~ xs ~ _ => Word(deflate(xs))}           | rep(' ') ~ (chrExcept(' ', EofCh)+)           ^^ {case _ ~ xs     => Word(xs mkString "")}         );                 private def deflate(xs : List[Any]) : String = xs match {             case (bs ~ c) :: ys => c.toString + deflate(ys)             case y :: ys => y + deflate(ys)             case _ => ""         }     }         var scanner = new Lexer.Scanner(readLine)         while (!scanner.atEnd) {         scanner.first match {case Word(str) => if (isIsoPalin(str.toList.filter {_ != ' '} )) println(str)}         scanner = scanner.rest     } }

Edit: fixed some bugs, cleaned up code.