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marionebl's solution

to Custom Set in the OCaml Track

Published at Jul 01 2019 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution was written.

Create a custom set type.

Sometimes it is necessary to define a custom data structure of some type, like a set. In this exercise you will define your own set. How it works internally doesn't matter, as long as it behaves like a set of unique elements.

Getting Started

  1. Install the Exercism CLI.

  2. Install OCaml.

  3. For library documentation, follow Useful OCaml resources.

Running Tests

A Makefile is provided with a default target to compile your solution and run the tests. At the command line, type:

make

Submitting Incomplete Solutions

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Feedback, Issues, Pull Requests

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If you have feedback about an exercise, or want to help implementing a new one, head over there and create an issue or submit a PR. We welcome new contributors!

test.ml

open OUnit2

module type EXPECTED = sig
  type t
  val of_list : int list -> t
  val is_empty : t -> bool
  val is_member : t -> int -> bool
  val is_subset : t -> t -> bool
  val is_disjoint: t -> t -> bool
  val equal : t -> t -> bool
  val add : t -> int -> t
  val intersect : t -> t -> t
  val difference : t -> t -> t
  val union : t -> t -> t
end

module CSet : EXPECTED = Custom_set.Make(struct
  type t = int
  let compare a b = compare (a mod 10) (b mod 10)
end)

let assert_true exp _text_ctxt = assert_equal exp true
let assert_false exp _text_ctxt = assert_equal exp false
let tests = [
  "sets with no elements are empty">::
    assert_true (CSet.is_empty (CSet.of_list []));
  "sets with elements are not empty">::
    assert_false (CSet.is_empty (CSet.of_list [1]));
  "nothing is contained in the empty set">::
    assert_false (CSet.is_member (CSet.of_list []) 1);
  "when the element is in the set">::
    assert_true (CSet.is_member (CSet.of_list [1;2;3]) 1);
  "when the element is not in the set">::
    assert_false (CSet.is_member (CSet.of_list [1;3;3]) 4);
  "empty set is a subset of an other empty set">::
    assert_true (CSet.is_subset (CSet.of_list []) (CSet.of_list []));
  "empty set is a subset of a non empty set">::
    assert_true (CSet.is_subset (CSet.of_list []) (CSet.of_list [1]));
  "non-empty set is a not subset of an empty set">::
    assert_false (CSet.is_subset (CSet.of_list [1]) (CSet.of_list []));
  "set is a subset of set with exact same elements">::
    assert_true (CSet.is_subset (CSet.of_list [1;2;3]) (CSet.of_list [1;2;3]));
  "set is a subset of larger set with exact same elements">::
    assert_true (CSet.is_subset (CSet.of_list [1;2;3]) (CSet.of_list [4;1;2;3]));
  "set is not a subset of set that does not contain its elements">::
    assert_false (CSet.is_subset (CSet.of_list [1;2;3]) (CSet.of_list [4;1;3]));
  "the empty set is disjoint with itself">::
    assert_true (CSet.is_disjoint (CSet.of_list []) (CSet.of_list []));
  "the empty set is disjoint with non-empty set">::
    assert_true (CSet.is_disjoint (CSet.of_list []) (CSet.of_list [1]));
  "non-empty set is disjoint with empty set">::
    assert_true (CSet.is_disjoint (CSet.of_list [1]) (CSet.of_list []));
  "sets are not disjoint if they share an element">::
    assert_false (CSet.is_disjoint (CSet.of_list [1;2]) (CSet.of_list [2;3]));
  "sets are disjoint if they do not share an element">::
    assert_true (CSet.is_disjoint (CSet.of_list [1;2]) (CSet.of_list [3;4]));
  "empty sets are equal">::
    assert_true (CSet.equal (CSet.of_list []) (CSet.of_list []));
  "empty set is not equal to non-empty set">::
    assert_false (CSet.equal (CSet.of_list []) (CSet.of_list [1;2;3]));
  "non-empty set is not equal to empty set">::
    assert_false (CSet.equal (CSet.of_list [1;2;3]) (CSet.of_list []));
  "sets with the same elements are equal">::
    assert_true (CSet.equal (CSet.of_list [1;2]) (CSet.of_list [2;1]));
  "sets with different elements are not equal">::
    assert_false (CSet.equal (CSet.of_list [1;2;3]) (CSet.of_list [1;2;4]));
  "add to empty set">::
    assert_true (CSet.equal (CSet.of_list [3]) (CSet.add (CSet.of_list []) 3));
  "add to non-empty set">::
    assert_true (CSet.equal (CSet.of_list [1;2;3;4]) (CSet.add (CSet.of_list [1;2;4]) 3));
  "adding existing element does not change set">::
    assert_true (CSet.equal (CSet.of_list [1;2;3]) (CSet.add (CSet.of_list [1;2;3]) 3));
  "intersection of two empty sets is empty set">::
    assert_true (CSet.equal (CSet.of_list []) (CSet.intersect (CSet.of_list []) (CSet.of_list [])));
  "intersection of empty set with non-empty set is an empty set">::
    assert_true (CSet.equal (CSet.of_list []) (CSet.intersect (CSet.of_list []) (CSet.of_list [3;2;5])));
  "intersection of non-empty set with empty set is an empty set">::
    assert_true (CSet.equal (CSet.of_list []) (CSet.intersect (CSet.of_list [1;2;3;4]) (CSet.of_list [])));
  "intersection of sets with no shared elements is empty set">::
    assert_true (CSet.equal (CSet.of_list []) (CSet.intersect (CSet.of_list [1;2;3]) (CSet.of_list [4;5;6])));
  "intersection of set with shared elements is set of shared elements">::
    assert_true (CSet.equal (CSet.of_list [2;3]) (CSet.intersect (CSet.of_list [1;2;3;4]) (CSet.of_list [3;2;5])));
  "difference of two empty sets is an empty set">::
    assert_true (CSet.equal (CSet.of_list []) (CSet.difference (CSet.of_list []) (CSet.of_list [])));
  "difference of empty set and non-empty set is empty set">::
    assert_true (CSet.equal (CSet.of_list []) (CSet.difference (CSet.of_list []) (CSet.of_list [3;2;5])));
  "difference of non-empty set and empty set is the non-empty set">::
    assert_true (CSet.equal (CSet.of_list [1;2;3;4]) (CSet.difference (CSet.of_list [1;2;3;4]) (CSet.of_list [])));
  "difference of two non-empty sets is the sets of elements only in the first set">::
    assert_true (CSet.equal (CSet.of_list [1;3]) (CSet.difference (CSet.of_list [3;2;1]) (CSet.of_list [2;4])));
  "union of two empty sets is an empty set">::
    assert_true (CSet.equal (CSet.of_list []) (CSet.union (CSet.of_list []) (CSet.of_list [])));
  "union of empty set and non-empty set is non-empty set">::
    assert_true (CSet.equal (CSet.of_list [2]) (CSet.union (CSet.of_list []) (CSet.of_list [2])));
  "union of non-empty set and empty set is the non-empty set">::
    assert_true (CSet.equal (CSet.of_list [1;3]) (CSet.union (CSet.of_list [1;3]) (CSet.of_list [])));
  "union of two non-empty sets contains all unique elements">::
    assert_true (CSet.equal (CSet.of_list [1;2;3]) (CSet.union (CSet.of_list [1;3]) (CSet.of_list [2;3])));
  ]

let () =
  run_test_tt_main ("custom_set tests" >::: tests)
open Base

module type ELEMENT = sig
    type t
    val compare : t -> t -> int
end

module Make(El: ELEMENT) = struct
    type t = El.t list
    type el = El.t

    let el_equal m m' = 
      Int.(El.compare m m' = 0)

    let is_empty = List.is_empty

    let is_member s m = 
      List.exists s ~f:(el_equal m)

    let is_subset s s' =
      List.for_all s ~f:(is_member s')

    let is_disjoint s s' = 
      List.for_all s ~f:(is_member s' |> Fn.non)

    let equal s s' =
      Int.(List.length s = List.length s') && is_subset s s'
      
    let add s e =
      if is_member s e then
        s
      else 
        List.append s [e]

    let difference s s' = 
      List.filter s ~f:(is_member s' |> Fn.non)

    let intersect s s' = 
      List.filter s ~f:(is_member s')

    let rec union s = function
      | [] -> s
      | h::t when is_member s h -> union s t
      | h::t -> union (s @ [h]) t

    let of_list l = union [] l
end

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