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nganhkhoa's solution

to Bracket Push in the PureScript Track

Published at Oct 30 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.Maybe (Maybe(..), fromJust)
import Data.List (List(..), (:), foldl, length, head, tail, snoc, insertAt)
import Data.String.CodeUnits (toCharArray)
import Partial.Unsafe (unsafePartial)

data BracketType
  = Round
  | Square
  | Curly

derive instance eqBracketType :: Eq BracketType

type Bracket = {
  type :: BracketType,
  enclosed :: Boolean
}

parseChar :: Char -> Maybe Bracket
parseChar c
  | c == '{' = Just { type: Curly,  enclosed: false }
  | c == '(' = Just { type: Round,  enclosed: false }
  | c == '[' = Just { type: Square, enclosed: false }
  | c == ']' = Just { type: Square, enclosed: true  }
  | c == ')' = Just { type: Round,  enclosed: true  }
  | c == '}' = Just { type: Curly,  enclosed: true  }
  | otherwise = Nothing

stackBracket :: Maybe (List Bracket) -> Maybe Bracket -> Maybe (List Bracket)
stackBracket acc (Nothing) = acc
stackBracket (Nothing) (Just c) = Just (c : Nil)
stackBracket (Just acc) (Just c@{type: _, enclosed: false}) = insertAt 0 c acc
stackBracket (Just acc) (Just c@{type: _, enclosed: true}) =
  if (checkHead c listHead) then
    tail acc
  else
    Just (snoc acc (unsafePartial (fromJust listHead)))
  where
  listHead :: Maybe Bracket
  listHead = head acc
  checkHead :: Bracket -> Maybe Bracket -> Boolean
  checkHead ch (Just hd) = ch.type == hd.type
  checkHead _ _ = false


isPaired :: String -> Boolean
isPaired "" = true
isPaired expr =
  case stack of
    Nothing -> false
    (Just s) -> eq 0 $ length s
  where
    stack =
      foldl stackBracket Nothing
      $ map parseChar
      $ toCharArray expr

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