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ryanplusplus's solution

to Custom Set in the Lua Track

Published at Jul 13 2018 · 1 comment
Instructions
Test suite
Solution

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.

Running the tests

To run the tests, run the command busted from within the exercise directory.

Further information

For more detailed information about the Lua track, including how to get help if you're having trouble, please visit the exercism.io Lua language page.

Submitting Incomplete Solutions

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

custom-set_spec.lua

local Set = require('custom-set')

describe('custom-set', function()
  describe('is_empty', function()
    it('should indicate that an empty set is empty', function()
      assert.is_true(Set():is_empty())
    end)

    it('should indicate that sets with elemnts are non-empty', function()
      assert.is_false(Set(1):is_empty())
    end)
  end)

  describe('contains', function()
    it('should indicate that nothing is an element of an empty set', function()
      assert.is_false(Set():contains(1))
    end)

    it('should indicate that an element is contained in a set that contains the element', function()
      assert.is_true(Set(1, 2, 3):contains(1))
      assert.is_true(Set(1, 2, 3):contains(2))
      assert.is_true(Set(1, 2, 3):contains(3))
    end)

    it('should indicate that an element that is not in a set is not contained in the set', function()
      assert.is_false(Set(1, 2, 3):contains(4))
    end)
  end)

  describe('is_subset', function()
    it('should indicate that an empty set is a subset of another empty set', function()
      assert.is_true(Set():is_subset(Set()))
    end)

    it('should indicate that an empty set is a subset of a non-empty set', function()
      assert.is_true(Set():is_subset(Set(1)))
    end)

    it('should indicate that a non-empty set is not a subset of an empty set', function()
      assert.is_false(Set(1):is_subset(Set()))
    end)

    it('should indicate that a non-empty set is a subset of itself', function()
      assert.is_true(Set(1, 2, 3):is_subset(Set(1, 2, 3)))
    end)

    it('should indicate that a proper subset is a subset', function()
      assert.is_true(Set(1, 2, 3):is_subset(Set(4, 1, 2, 3)))
    end)

    it('should indicate that a set is not a subset of another set with different elements but the same element count', function()
      assert.is_false(Set(1, 2, 3):is_subset(Set(4, 1, 3)))
    end)
  end)

  describe('is_disjoint', function()
    it('should indicate that the empty set is disjoint with itself', function()
      assert.is_true(Set():is_disjoint(Set()))
    end)

    it('should indicate that the empty set is disjoint with a non-empty set', function()
      assert.is_true(Set():is_disjoint(Set(1)))
    end)

    it('should indicate that a non-empty set is not disjoint with an empty set', function()
      assert.is_true(Set(1):is_disjoint(Set()))
    end)

    it('should indicate that sets with an element in common are not disjoint', function()
      assert.is_false(Set(1, 2):is_disjoint(Set(2, 3)))
    end)

    it('should indicate that sets with no elements in common are disjoint', function()
      assert.is_true(Set(1, 2):is_disjoint(Set(3, 4)))
    end)
  end)

  describe('equality', function()
    it('should consider empty sets equal', function()
      assert.is_true(Set():equals(Set()))
    end)

    it('should not consider an empty set to be equal to a non-empty set', function()
      assert.is_false(Set():equals(Set(1, 2, 3)))
    end)

    it('should not consider a non-empty set to be equal to an empty set', function()
      assert.is_false(Set(1, 2, 3):equals(Set()))
    end)

    it('should ignore order', function()
      assert.is_true(Set(1, 3):equals(Set(3, 1)))
    end)

    it('should consider different sets to be different', function()
      assert.is_false(Set(1, 2, 3):equals(Set(1, 2, 4)))
    end)
  end)

  describe('add', function()
    it('should allow an element to be added to an empty set', function()
      local s = Set()
      s:add(3)
      assert.is_true(s:contains(3))
    end)

    it('should allow an element to be added to a non-empty set', function()
      local s = Set(1, 2, 4)
      s:add(3)
      assert.is_true(s:equals(Set(1, 2, 3, 4)))
    end)

    it('should allow an element to be re-added to a set', function()
      local s = Set(1, 2, 3)
      s:add(3)
      assert.is_true(s:equals(Set(1, 2, 3)))
    end)
  end)

  describe('intersection', function()
    it('should give the empty set as the intersection of two empty sets', function()
      assert.is_true(Set():intersection(Set()):equals(Set()))
    end)

    it('should intersect an empty set with a non-empty set', function()
      assert.is_true(Set():intersection(Set(3, 2, 5)):equals(Set()))
    end)

    it('should intersect a non-empty set with an empty set', function()
      assert.is_true(Set(1, 2, 3, 4):intersection(Set()):equals(Set()))
    end)

    it('should intersect a single element set with itself', function()
      assert.is_true(Set(3):intersection(Set(3)):equals(Set(3)))
    end)

    it('should intersect sets with a single element in common', function()
      assert.is_true(Set(1, 2, 3):intersection(Set(3, 4, 5)):equals(Set(3)))
    end)

    it('should intersect sets with a multiple elements in common', function()
      assert.is_true(Set(1, 2, 3, 4):intersection(Set(3, 2, 5)):equals(Set(2, 3)))
    end)

    it('should intersect a set with a subset', function()
      assert.is_true(Set(1, 2, 3):intersection(Set(2, 3)):equals(Set(2, 3)))
    end)

    it('should intersect sets with no elements in common', function()
      assert.is_true(Set(1, 2, 3):intersection(Set(4, 5, 6)):equals(Set()))
    end)
  end)

  describe('intersection', function()
    it('should give the empty set as the intersection of two empty sets', function()
      assert.is_true(Set():intersection(Set()):equals(Set()))
    end)

    it('should intersect an empty set with a non-empty set', function()
      assert.is_true(Set():intersection(Set(3, 2, 5)):equals(Set()))
    end)

    it('should intersect a non-empty set with an empty set', function()
      assert.is_true(Set(1, 2, 3, 4):intersection(Set()):equals(Set()))
    end)

    it('should intersect a single element set with itself', function()
      assert.is_true(Set(3):intersection(Set(3)):equals(Set(3)))
    end)

    it('should intersect sets with a single element in common', function()
      assert.is_true(Set(1, 2, 3):intersection(Set(3, 4, 5)):equals(Set(3)))
    end)

    it('should intersect sets with a multiple elements in common', function()
      assert.is_true(Set(1, 2, 3, 4):intersection(Set(3, 2, 5)):equals(Set(2, 3)))
    end)

    it('should intersect a set with a subset', function()
      assert.is_true(Set(1, 2, 3):intersection(Set(2, 3)):equals(Set(2, 3)))
    end)

    it('should intersect sets with no elements in common', function()
      assert.is_true(Set(1, 2, 3):intersection(Set(4, 5, 6)):equals(Set()))
    end)
  end)

  describe('difference', function()
    it('should give the difference of two empty sets as the empty set', function()
      assert.is_true(Set():difference(Set()):equals(Set()))
    end)

    it('should give the difference of an empty set and a non-empty set as the empty set', function()
      assert.is_true(Set():difference(Set(3, 2, 5)):equals(Set()))
    end)

    it('should give the difference of a non-empty set and the empty set as the non-empty set', function()
      assert.is_true(Set(1, 2, 3, 4):difference(Set()):equals(Set(1, 2, 3, 4)))
    end)

    it('should give the difference of two sets with an intersection', function()
      assert.is_true(Set(3, 2, 1):difference(Set(2, 4)):equals(Set(1, 3)))
    end)
  end)

  describe('union', function()
    it('should produce the empty set as the union of two empty sets', function()
      assert.is_true(Set():union(Set()):equals(Set()))
    end)

    it('should give the union of an empty set with another set as the other set', function()
      assert.is_true(Set():union(Set(2)):equals(Set(2)))
    end)

    it('should give the union of a non-empty set and an empty set as the non-empty set', function()
      assert.is_true(Set(1, 3):union(Set()):equals(Set(1, 3)))
    end)

    it('should produce the union of different sets', function()
      assert.is_true(Set(1, 3):union(Set(2, 3)):equals(Set(1, 2, 3)))
    end)
  end)
end)
local Set = {}
Set.__index = Set

local function create(...)
  local o = { _contents = {} }
  for _, v in ipairs(table.pack(...)) do
    o._contents[v] = true
  end
  return setmetatable(o, Set)
end

function Set:equals(other)
  return self:is_subset(other) and other:is_subset(self)
end

function Set:add(element)
  self._contents[element] = true
end

function Set:remove(element)
  self._contents[element] = nil
end

function Set:is_empty()
  return self:equals(create())
end

function Set:size()
  local size = 0
  for _ in pairs(self._contents) do
    size = size + 1
  end
  return size
end

function Set:contains(element)
  return self._contents[element] ~= nil
end

function Set:is_subset(other)
  for k in pairs(self._contents) do
    if not other:contains(k) then return false end
  end
  return true
end

function Set:is_disjoint(other)
  return self:intersection(other):is_empty()
end

function Set:intersection(other)
  local intersection = create()
  for k in pairs(self._contents) do
    if other:contains(k) then intersection:add(k) end
  end
  return intersection
end

function Set:union(other)
  local union = create()
  for k in pairs(self._contents) do
    union:add(k)
  end
  for k in pairs(other._contents) do
    union:add(k)
  end
  return union
end

function Set:difference(other)
  local difference = self:union(create())
  for k in pairs(other._contents) do
    difference:remove(k)
  end
  return difference
end

function Set:symmetric_difference(other)
  local symmetric_difference = create()
  for k in pairs(self._contents) do
    if not other:contains(k) then symmetric_difference:add(k) end
  end
  for k in pairs(other._contents) do
    if not self:contains(k) then symmetric_difference:add(k) end
  end
  return symmetric_difference
end

return create

Community comments

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Avatar of ryanplusplus

I realized that is_disjoint is the same as having an empty intersection.

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