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git-in-my-anus's solution

to Bracket Push in the PureScript Track

Published at Jul 28 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.Foldable (foldl)
import Data.List (List(..), (:))
import Data.Maybe (Maybe(..))
import Data.String (toCharArray)
import Data.Tuple (Tuple(..))

data Stack a = Stack (List a)

push :: forall a. Stack a -> a -> Stack a
push (Stack l) el = Stack (el : l)

pop :: forall a. Stack a -> Tuple (Maybe a) (Stack a)
pop (Stack Nil) = Tuple Nothing (Stack Nil)
pop (Stack (x : xs)) = Tuple (Just x) (Stack xs)


type Bracket =
  { btype :: BType
  , direction :: Direction
  }

data BType = Curly | Square | Parens
derive instance eqBType :: Eq BType

data Direction = Open | Closed

charToBracket :: Char -> Maybe Bracket
charToBracket '{' = Just { btype: Curly, direction: Open }
charToBracket '[' = Just { btype: Square, direction: Open }
charToBracket '(' = Just { btype: Parens, direction: Open }
charToBracket '}' = Just { btype: Curly, direction: Closed }
charToBracket ']' = Just { btype: Square, direction: Closed }
charToBracket ')' = Just { btype: Parens, direction: Closed }
charToBracket _ = Nothing


data Balance
  = OpenImbalanced (Stack Bracket)
  | ClosedImbalanced

isPaired :: String -> Boolean
isPaired s =
  case checkBalance of
    OpenImbalanced (Stack Nil) -> true
    _ -> false
  where
    checkBalance = foldl updateBalance (OpenImbalanced (Stack Nil)) (toCharArray s)

updateBalance :: Balance ->  Char -> Balance
updateBalance ClosedImbalanced _ = ClosedImbalanced
updateBalance (OpenImbalanced brackets) c =
  case charToBracket c, pop brackets of
    Just { direction: Closed }, (Tuple Nothing _) -> ClosedImbalanced
    Just { direction: Closed, btype }, (Tuple (Just topBracket) rest)
      | btype == topBracket.btype -> OpenImbalanced rest
      | otherwise -> ClosedImbalanced
    Just b@{ direction: Open, btype }, _ -> OpenImbalanced $ push brackets b
    Nothing, _ -> OpenImbalanced brackets

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