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to Sublist in the Haskell Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Given two lists determine if the first list is contained within the second list, if the second list is contained within the first list, if both lists are contained within each other or if none of these are true.

Specifically, a list A is a sublist of list B if by dropping 0 or more elements from the front of B and 0 or more elements from the back of B you get a list that's completely equal to A.

Examples:

  • A = [1, 2, 3], B = [1, 2, 3, 4, 5], A is a sublist of B
  • A = [3, 4, 5], B = [1, 2, 3, 4, 5], A is a sublist of B
  • A = [3, 4], B = [1, 2, 3, 4, 5], A is a sublist of B
  • A = [1, 2, 3], B = [1, 2, 3], A is equal to B
  • A = [1, 2, 3, 4, 5], B = [2, 3, 4], A is a superlist of B
  • A = [1, 2, 4], B = [1, 2, 3, 4, 5], A is not a superlist of, sublist of or equal to B

Hints

To complete this exercise, you need to implement the sublist function.

Getting Started

For installation and learning resources, refer to the exercism help page.

Running the tests

To run the test suite, execute the following command:

stack test

If you get an error message like this...

No .cabal file found in directory

You are probably running an old stack version and need to upgrade it.

Otherwise, if you get an error message like this...

No compiler found, expected minor version match with...
Try running "stack setup" to install the correct GHC...

Just do as it says and it will download and install the correct compiler version:

stack setup

Running GHCi

If you want to play with your solution in GHCi, just run the command:

stack ghci

Feedback, Issues, Pull Requests

The exercism/haskell repository on GitHub is the home for all of the Haskell exercises.

If you have feedback about an exercise, or want to help implementing a new one, head over there and create an issue. We'll do our best to help you!

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

Tests.hs

{-# LANGUAGE RecordWildCards #-}

import Data.Foldable     (for_)
import Test.Hspec        (Spec, describe, it, shouldBe)
import Test.Hspec.Runner (configFastFail, defaultConfig, hspecWith)

import Sublist (Sublist(Equal,Sublist,Superlist,Unequal), sublist)

main :: IO ()
main = hspecWith defaultConfig {configFastFail = True} specs

specs :: Spec
specs = do
          describe "standard tests" $ for_ cases test
          describe "track specific tests" $ do

            let xs = replicate 1000 'x'

            it "compare larger equal lists" $
              sublist xs xs
              `shouldBe` Equal

            it "sublist early in huge list" $
              sublist [3, 4, 5] [1..1000000 :: Int]
              `shouldBe` Sublist

            it "huge sublist not in huge list" $
              sublist [10..1000001] [1..1000000 :: Int]
              `shouldBe` Unequal

            it "superlist early in huge list" $
              sublist [1..1000000] [3, 4, 5 :: Int]
              `shouldBe` Superlist
  where

    test Case{..} = it explanation assertion
      where
        assertion   = sublist listOne listTwo `shouldBe` expectation
        explanation = unwords [ "sublist"
                              , show listOne
                              , show listTwo
                              , "-"
                              , description ]

data Case = Case { description :: String
                 , listOne     :: [Integer]
                 , listTwo     :: [Integer]
                 , expectation :: Sublist
                 }

cases :: [Case]
cases = [ Case { description = "empty lists"
               , listOne     = []
               , listTwo     = []
               , expectation = Equal
               }
        , Case { description = "empty list within non empty list"
               , listOne     = []
               , listTwo     = [1, 2, 3]
               , expectation = Sublist
               }
        , Case { description = "non empty list contains empty list"
               , listOne     = [1, 2, 3]
               , listTwo     = []
               , expectation = Superlist
               }
        , Case { description = "list equals itself"
               , listOne     = [1, 2, 3]
               , listTwo     = [1, 2, 3]
               , expectation = Equal
               }
        , Case { description = "different lists"
               , listOne     = [1, 2, 3]
               , listTwo     = [2, 3, 4]
               , expectation = Unequal
               }
        , Case { description = "false start"
               , listOne     = [1, 2, 5]
               , listTwo     = [0, 1, 2, 3, 1, 2, 5, 6]
               , expectation = Sublist
               }
        , Case { description = "consecutive"
               , listOne     = [1, 1, 2]
               , listTwo     = [0, 1, 1, 1, 2, 1, 2]
               , expectation = Sublist
               }
        , Case { description = "sublist at start"
               , listOne     = [0, 1, 2]
               , listTwo     = [0, 1, 2, 3, 4, 5]
               , expectation = Sublist
               }
        , Case { description = "sublist in middle"
               , listOne     = [2, 3, 4]
               , listTwo     = [0, 1, 2, 3, 4, 5]
               , expectation = Sublist
               }
        , Case { description = "sublist at end"
               , listOne     = [3, 4, 5]
               , listTwo     = [0, 1, 2, 3, 4, 5]
               , expectation = Sublist
               }
        , Case { description = "at start of superlist"
               , listOne     = [0, 1, 2, 3, 4, 5]
               , listTwo     = [0, 1, 2]
               , expectation = Superlist
               }
        , Case { description = "in middle of superlist"
               , listOne     = [0, 1, 2, 3, 4, 5]
               , listTwo     = [2, 3]
               , expectation = Superlist
               }
        , Case { description = "at end of superlist"
               , listOne     = [0, 1, 2, 3, 4, 5]
               , listTwo     = [3, 4, 5]
               , expectation = Superlist
               }
        , Case { description = "first list missing element from second list"
               , listOne     = [1, 3]
               , listTwo     = [1, 2, 3]
               , expectation = Unequal
               }
        , Case { description = "second list missing element from first list"
               , listOne     = [1, 2, 3]
               , listTwo     = [1, 3]
               , expectation = Unequal
               }
        , Case { description = "order matters to a list"
               , listOne     = [1, 2, 3]
               , listTwo     = [3, 2, 1]
               , expectation = Unequal
               }
        , Case { description = "same digits but different numbers"
               , listOne     = [1, 0, 1]
               , listTwo     = [10, 1]
               , expectation = Unequal
               }
        ]
module Sublist (Sublist(..), sublist) where

import Data.List

data Sublist = Equal | Sublist | Superlist | Unequal
  deriving (Eq, Show)

sublist ::Eq a => [a] -> [a] -> Sublist
sublist a b
  | a == b = Equal
  | isInfixOf a b = Sublist
  | isInfixOf b a = Superlist
  | otherwise = Unequal

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