Solve 217 - Contains Duplicate (#7)

Author: terenceponce

README.md

@@ -9,3 +9,4 @@ This is a monorepo containing my solutions to LeetCode problems written in vario
 ## List of Problems/Solutions
 
 - 1 - Two Sum - [Notes](notes/0001_two_sum.md) | [Elixir](elixir/lib/solutions/0001_two_sum/two_sum.ex) | [Ruby](ruby/lib/solutions/0001_two_sum/two_sum.rb)
+- 217 - Contains Duplicate - [Notes](notes/0217_contains_duplicate.md) | [Elixir](elixir/lib/solutions/0217_contains_duplicate/contains_duplicate.ex) | [Ruby](ruby/lib/solutions/0217_contains_duplicate/contains_duplicate.rb)

elixir/lib/solutions/0217_contains_duplicate/contains_duplicate.ex

@@ -0,0 +1,14 @@
+defmodule LeetCode.Solutions.ContainsDuplicate do
+  @moduledoc false
+
+  @spec call([integer()]) :: boolean
+  def call(nums) do
+    Enum.reduce_while(nums, MapSet.new(), fn num, set ->
+      if MapSet.member?(set, num) do
+        {:halt, true}
+      else
+        {:cont, MapSet.put(set, num)}
+      end
+    end) == true
+  end
+end

elixir/test/solutions/0217_contains_duplicate/contains_duplicate_test.exs

@@ -0,0 +1,25 @@
+defmodule LeetCode.Solutions.ContainsDuplicateTest do
+  use ExUnit.Case, async: true
+
+  alias LeetCode.Solutions.ContainsDuplicate
+
+  test "Case 1 works" do
+    assert ContainsDuplicate.call([1, 2, 3, 1]) == true
+  end
+
+  test "Case 2 works" do
+    assert ContainsDuplicate.call([1, 2, 3, 4]) == false
+  end
+
+  test "Case 3 works" do
+    assert ContainsDuplicate.call([1, 1, 1, 3, 3, 4, 3, 2, 4, 2]) == true
+  end
+
+  test "Edge Case 1 works" do
+    assert ContainsDuplicate.call([3, 3]) == true
+  end
+
+  test "Edge Case 2 works" do
+    assert ContainsDuplicate.call([0, 4, 5, 0, 3, 6]) == true
+  end
+end

notes/0217_contains_duplicate.md

@@ -0,0 +1,52 @@
+# Contains Duplicate
+
+**Link to Problem**: https://leetcode.com/problems/contains-duplicate
+
+## Solutions
+
+- [Elixir](../elixir/lib/solutions/0217_contains_duplicate/contains_duplicate.ex)
+- [Ruby](../ruby/lib/solutions/0217_contains_duplicate/contains_duplicate.rb)
+
+## Description
+
+Given an integer array nums, return true if any value appears at least twice in the array,
+and return false if every element is distinct.
+
+## Examples
+
+### Example 1
+
+```
+Input: nums = [1,2,3,1]
+Output: true
+```
+
+### Example 2
+
+```
+Input: nums = [1,2,3,4]
+Output: false
+```
+
+### Example 3
+
+```
+Input: nums = [1,1,1,3,3,4,3,2,4,2]
+Output: true
+```
+
+## Approach
+
+The trick is to iterate through the list/array and immediately return `true` once we get a
+duplicate. If not, we then return `false`.
+
+We can determine duplicates by using a hash map or set. We store the value to the data structure
+as we go along the list and hitting an existing member/attribute means that we have a duplicate.
+
+## Thoughts
+
+The solution for Ruby is a lot more simple because Ruby allows early `return` that will
+immediately halt the method.
+
+For Elixir, it is possible to do the same thing through `Enum.reduce_while`, but the runtime
+is so different across both of them.

ruby/lib/solutions/0217_contains_duplicate/contains_duplicate.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+def contains_duplicate(nums)
+  hash = {}
+
+  nums.each do |num|
+    return true if hash[num]
+
+    hash[num] = 1
+  end
+
+  false
+end

ruby/test/solutions/0217_contains_duplicate/contains_duplicate_test.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+require_relative '../../../lib/solutions/0217_contains_duplicate/contains_duplicate'
+
+class ContainsDuplicateTest < Minitest::Test
+  def test_case_1_works
+    assert contains_duplicate([1, 2, 3, 1])
+  end
+
+  def test_case_2_works
+    refute contains_duplicate([1, 2, 3, 4])
+  end
+
+  def test_case_3_works
+    assert contains_duplicate([1, 1, 1, 3, 3, 4, 3, 2, 4, 2])
+  end
+end