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stefanscheidt's solution

to Bracket Push in the PureScript Track

Published at Mar 25 2019 · 0 comments
Instructions
Test suite
Solution

Given a string containing brackets [], braces {} and parentheses (), verify that all the pairs are matched and nested correctly.

Source

Ginna Baker

Submitting Incomplete Solutions

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Main.purs

module Test.Main where

import Prelude

import Effect (Effect)
import Test.Unit.Assert as Assert
import Test.Unit (TestSuite, suite, test)
import Test.Unit.Main (runTest)
import BracketPush (isPaired)

main :: Effect Unit
main = runTest suites

suites :: TestSuite
suites = do
  suite "BracketPush.isPaired" do

    test "paired square brackets" $
      Assert.equal true
                   (isPaired "[]")

    test "empty string" $
      Assert.equal true
                   (isPaired "")

    test "unpaired brackets" $
      Assert.equal false
                   (isPaired "[[")

    test "wrong ordered brackets" $
      Assert.equal false
                   (isPaired "}{")

    test "paired with whitespace" $
      Assert.equal true
                   (isPaired "{ }")

    test "simple nested brackets" $
      Assert.equal true
                   (isPaired "{[]}")

    test "several paired brackets" $
      Assert.equal true
                   (isPaired "{}[]")

    test "paired and nested brackets" $
      Assert.equal true
                   (isPaired "([{}({}[])])")

    test "unopened closing brackets" $
      Assert.equal false
                   (isPaired "{[)][]}")

    test "unpaired and nested brackets" $
      Assert.equal false
                   (isPaired "([{])")

    test "paired and wrong nested brackets" $
      Assert.equal false
                   (isPaired "[({]})")

    test "math expression" $
      Assert.equal true
                   (isPaired "(((185 + 223.85) * 15) - 543)/2")

    test "complex latex expression" $
      Assert.equal true
                   (isPaired "\\left(\\begin{array}{cc} \\frac{1}{3} & x\\\\ \\mathrm{e}^{x} &... x^2 \\end{array}\\right)")
module BracketPush
  ( isPaired
  ) where

import Prelude

import Data.Foldable (elem)
import Data.List (List(..), filter, fromFoldable, head, tail)
import Data.Maybe (Maybe(..))
import Data.String.CodeUnits (toCharArray)


isPaired :: String -> Boolean
isPaired = eq (Just Nil) <<< parse <<< normalize

normalize :: String -> List Char
normalize = filter isBracket <<< fromFoldable <<< toCharArray

parse :: List Char -> Maybe (List Char)
parse Nil = Just Nil
parse (Cons '(' xs) = parseBrackets ')' xs
parse (Cons '[' xs) = parseBrackets ']' xs
parse (Cons '{' xs) = parseBrackets '}' xs
parse inp@(Cons x xs)
  | elem x [']','}', ')'] = Just inp
  | otherwise             = Nothing

parseBrackets :: Char -> List Char -> Maybe (List Char)
parseBrackets close xs = do
    subtree <- parse xs
    headElem <- head subtree
    if headElem == close
      then tail subtree >>= parse
      else Nothing

isBracket :: Char -> Boolean
isBracket = flip elem brackets
  where
    brackets = toCharArray "(){}[]"

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