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revazi's solution

to Bracket Push in the PureScript Track

Published at Oct 10 2018 · 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

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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.List (List(..), fromFoldable)
import Data.Maybe (Maybe(..))
import Data.String.CodeUnits (toCharArray)


data Bracket
  = SquareBracket
  | RoundedBracket
  | CurlyBracket
  | AngleBracket

derive instance eqBracket :: Eq Bracket

openBracket :: Char -> Maybe Bracket
openBracket '[' = Just SquareBracket
openBracket '(' = Just RoundedBracket
openBracket '{' = Just CurlyBracket
openBracket '<' = Just AngleBracket
openBracket _ = Nothing

closeBracket :: Char -> Maybe Bracket
closeBracket ']' = Just SquareBracket
closeBracket ')' = Just RoundedBracket
closeBracket '}' = Just CurlyBracket
closeBracket '>' = Just AngleBracket
closeBracket _ = Nothing

isPaired :: String -> Boolean
isPaired a = isPaired' Nil $ fromFoldable (toCharArray a)

isPaired' :: List Bracket -> List Char -> Boolean
isPaired' bs Nil = case bs of
  Nil -> true
  Cons _ _ -> false
isPaired' bs (Cons c cs) = case openBracket c of
  Just b -> isPaired' (Cons b bs) cs
  Nothing -> case closeBracket c of
    Just b -> case bs of
      Cons b' bs' -> if b == b'
        then isPaired' bs' cs
        else false
      Nil -> false
    Nothing -> isPaired' bs cs

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