From 3cca135e4e179e606f27f5507ce956124d6cd1e5 Mon Sep 17 00:00:00 2001
From: Onur ER <onurer34@hotmail.com.tr>
Date: Thu, 17 Oct 2019 12:26:54 +0300
Subject: [PATCH 01/32] Add the third problem from project Euler

Add the third problem from project Euler
---
 Project Euler/Problem 3/problem3_sol1.rb | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 Project Euler/Problem 3/problem3_sol1.rb

diff --git a/Project Euler/Problem 3/problem3_sol1.rb b/Project Euler/Problem 3/problem3_sol1.rb
new file mode 100644
index 0000000..30a8bca
--- /dev/null
+++ b/Project Euler/Problem 3/problem3_sol1.rb	
@@ -0,0 +1,19 @@
+# The prime factors of 13195 are 5, 7, 13 and 29.
+# What is the largest prime factor of the number 600851475143 ?
+
+def solution(n)
+  prime = 1
+  i = 2
+  while i * i <= n
+    while (n % i).zero?
+      prime = i
+      n = n.fdiv i
+    end
+    i += 1
+  end
+  prime = n if n > 1
+  prime.to_i
+end
+
+puts solution(600851475143)
+

From 2980dd73c123905dabd40071661dbacd7f04bbf2 Mon Sep 17 00:00:00 2001
From: Onur ER <onurer34@hotmail.com.tr>
Date: Fri, 18 Oct 2019 15:33:19 +0300
Subject: [PATCH 02/32] Add the fourth problem from project Euler

Add the fourth problem from project Euler
---
 Project Euler/Problem 4/problem4_sol1.rb | 11 +++++++++++
 1 file changed, 11 insertions(+)
 create mode 100644 Project Euler/Problem 4/problem4_sol1.rb

diff --git a/Project Euler/Problem 4/problem4_sol1.rb b/Project Euler/Problem 4/problem4_sol1.rb
new file mode 100644
index 0000000..fb1ac24
--- /dev/null
+++ b/Project Euler/Problem 4/problem4_sol1.rb	
@@ -0,0 +1,11 @@
+# A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
+# Find the largest palindrome made from the product of two 3-digit numbers.
+
+answer = 0
+999.downto(99) do |i|
+  999.downto(99) do |j|
+    t = (i * j)
+    answer = i * j if (t.to_s == t.to_s.reverse) && (t > answer) && (t > answer)
+  end
+end
+puts answer
\ No newline at end of file

From 86d482995335036ead05d0f3cd69c38b0dccc0e8 Mon Sep 17 00:00:00 2001
From: Onur ER <onurer34@hotmail.com.tr>
Date: Fri, 18 Oct 2019 15:37:07 +0300
Subject: [PATCH 03/32] Add the fourth problem from project Euler

Add the fourth problem from project Euler
---
 Project Euler/Problem 4/problem4_sol1.rb | 11 +++++++++++
 1 file changed, 11 insertions(+)
 create mode 100644 Project Euler/Problem 4/problem4_sol1.rb

diff --git a/Project Euler/Problem 4/problem4_sol1.rb b/Project Euler/Problem 4/problem4_sol1.rb
new file mode 100644
index 0000000..fb1ac24
--- /dev/null
+++ b/Project Euler/Problem 4/problem4_sol1.rb	
@@ -0,0 +1,11 @@
+# A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
+# Find the largest palindrome made from the product of two 3-digit numbers.
+
+answer = 0
+999.downto(99) do |i|
+  999.downto(99) do |j|
+    t = (i * j)
+    answer = i * j if (t.to_s == t.to_s.reverse) && (t > answer) && (t > answer)
+  end
+end
+puts answer
\ No newline at end of file

From 2f53abe79881392940bf80a227e6e693c2dc6741 Mon Sep 17 00:00:00 2001
From: vzvu3k6k <vzvu3k6k@gmail.com>
Date: Tue, 27 Oct 2020 05:35:41 +0900
Subject: [PATCH 04/32] Add tests for Sorting/bogo_sort.rb

---
 sorting/bogo_sort.rb      |  8 +++++---
 sorting/bogo_sort_test.rb | 16 ++++++++++++++++
 2 files changed, 21 insertions(+), 3 deletions(-)
 create mode 100644 sorting/bogo_sort_test.rb

diff --git a/sorting/bogo_sort.rb b/sorting/bogo_sort.rb
index c447cd5..c792026 100644
--- a/sorting/bogo_sort.rb
+++ b/sorting/bogo_sort.rb
@@ -13,6 +13,8 @@ class Array
   end
 end
 
-puts "Enter a list of numbers separated by space"
-str = gets.chomp.split('')
-puts str.bogosort.join('')
+if $0 == __FILE__
+  puts "Enter a list of numbers separated by space"
+  str = gets.chomp.split('')
+  puts str.bogosort.join('')
+end
diff --git a/sorting/bogo_sort_test.rb b/sorting/bogo_sort_test.rb
new file mode 100644
index 0000000..3fc6e83
--- /dev/null
+++ b/sorting/bogo_sort_test.rb
@@ -0,0 +1,16 @@
+require 'minitest/autorun'
+require_relative './bogo_sort'
+
+class TestBogoSort < Minitest::Test
+  def test_sorted_array
+    input = [1, 2, 3, 4, 5]
+    expected = input.dup
+    assert_equal expected, input.bogosort
+  end
+
+  def test_reversed_array
+    input = [5, 4, 3, 2, 1]
+    expected = [1, 2, 3, 4, 5]
+    assert_equal expected, input.bogosort
+  end
+end

From f3dc923ccb368551b6207188f702746e6c3bd93b Mon Sep 17 00:00:00 2001
From: vzvu3k6k <vzvu3k6k@gmail.com>
Date: Tue, 27 Oct 2020 05:41:54 +0900
Subject: [PATCH 05/32] Add Rakefile to run tests

---
 Rakefile | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 Rakefile

diff --git a/Rakefile b/Rakefile
new file mode 100644
index 0000000..d4dcdd1
--- /dev/null
+++ b/Rakefile
@@ -0,0 +1,7 @@
+require 'rake/testtask'
+
+Rake::TestTask.new(:test) do |t|
+  t.test_files = FileList['**/*_test.rb']
+end
+
+task default: :test

From 99b940ec8efda4c7abc0d1c630b106d82d562f3d Mon Sep 17 00:00:00 2001
From: vzvu3k6k <vzvu3k6k@gmail.com>
Date: Tue, 27 Oct 2020 05:42:18 +0900
Subject: [PATCH 06/32] Run tests on CI

---
 .github/workflows/test.yml | 12 ++++++++++++
 1 file changed, 12 insertions(+)
 create mode 100644 .github/workflows/test.yml

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..cfca6b2
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,12 @@
+name: test
+on: [push, pull_request]
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@master
+      - uses: actions/setup-ruby@master
+        with:
+          ruby-version: '2.7'
+      - name: Run tests
+        run: rake test

From d6e44e6afaedf9ff9cd90021fc7642424a6d0ed0 Mon Sep 17 00:00:00 2001
From: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Date: Sat, 14 Nov 2020 18:53:02 +0000
Subject: [PATCH 07/32] updating DIRECTORY.md

---
 DIRECTORY.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 48513cb..2fcb289 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -42,6 +42,7 @@
 
 ## Sorting
   * [Bogo Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bogo_sort.rb)
+  * [Bogo Sort Test](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bogo_sort_test.rb)
   * [Bubble Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bubble_sort.rb)
   * [Bucket Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bucket_sort.rb)
   * [Heap Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/heap_sort.rb)

From d24e95ae02dd2eed13501181cb3d69b350973959 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sat, 19 Dec 2020 20:18:06 -0800
Subject: [PATCH 08/32] Add brute force solution

---
 .../get_products_of_all_other_elements.rb     | 23 +++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 data_structures/arrays/get_products_of_all_other_elements.rb

diff --git a/data_structures/arrays/get_products_of_all_other_elements.rb b/data_structures/arrays/get_products_of_all_other_elements.rb
new file mode 100644
index 0000000..8bfe4a6
--- /dev/null
+++ b/data_structures/arrays/get_products_of_all_other_elements.rb
@@ -0,0 +1,23 @@
+# Arrays - Get Products of all other elements in Ruby
+
+# Algorithm challenge description:
+# Given an array of integers, return a new array such that
+# each element at index `i` of the new array is the product of
+# all the numbers in the original array except the one at `i`.
+
+# 1. Brute force solution
+def calculate_products_of_all_other_elements(nums)
+  products_other_elements = Array.new(nums.length, 1)
+
+  nums.each_with_index do |num1, i|
+    nums.each_with_index do |num2, j|
+      if (i != j)
+        products_other_elements[i] = products_other_elements[i] * num2
+      end
+    end
+  end
+
+  products_other_elements
+end
+
+puts(calculate_products_of_all_other_elements([1, 2, 3]))

From ecde337d9bab5665169c161f88345e0230a25226 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sat, 19 Dec 2020 20:18:22 -0800
Subject: [PATCH 09/32] Add better solution - O(n) time and space

---
 .../get_products_of_all_other_elements.rb     | 62 +++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/data_structures/arrays/get_products_of_all_other_elements.rb b/data_structures/arrays/get_products_of_all_other_elements.rb
index 8bfe4a6..b4a8a2f 100644
--- a/data_structures/arrays/get_products_of_all_other_elements.rb
+++ b/data_structures/arrays/get_products_of_all_other_elements.rb
@@ -21,3 +21,65 @@ def calculate_products_of_all_other_elements(nums)
 end
 
 puts(calculate_products_of_all_other_elements([1, 2, 3]))
+
+# 2. O(n) time and space
+# Arrays - Get Products of all other elements in Ruby
+
+# Generates prefix products
+def build_prefix_products(nums)
+  prefix_products = []
+
+  nums.each do |num|
+    if prefix_products.count > 0
+      prefix_products << (prefix_products.last * num)
+    else
+      prefix_products << num
+    end
+  end
+
+  return prefix_products
+end
+
+# Generates suffix products
+def build_suffix_products(nums)
+  suffix_products = []
+
+  nums.reverse.each do |num|
+    if suffix_products.count > 0
+      suffix_products << (suffix_products.last * num)
+    else
+      suffix_products << num
+    end
+  end
+
+  return suffix_products
+end
+
+# Builds output
+def output(prefix_products, suffix_products, nums)
+  result = []
+
+  nums.reverse.each_with_index do |num, index|
+    if index == 0
+      result << suffix_products[index + 1]
+    elsif index == nums.length - 1
+      result << prefix_products[index - 1]
+    else
+      result << (prefix_products[index - 1] * suffix_products[index + 1])
+    end
+  end
+
+  return result
+end
+
+# Generate result from the product of prefixes and suffixes
+def products(nums)
+  prefix_products = build_prefix_products(nums)
+  suffix_products = build_suffix_products(nums)
+  suffix_products = suffix_products.reverse
+
+  return output(prefix_products, suffix_products, nums)
+end
+
+puts(products([1, 2, 3]))
+# => [6, 3, 2]

From 13f9770de540fd3470623114358f6f6db99582e2 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sat, 19 Dec 2020 20:19:07 -0800
Subject: [PATCH 10/32] Add DIRECTORY.md entry

---
 DIRECTORY.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 48513cb..e2a7845 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -3,6 +3,8 @@
   * [Merkle Hellman Cryptosystem](https://github.com/TheAlgorithms/Ruby/blob/master/ciphers/merkle_hellman_cryptosystem.rb)
 
 ## Data Structures
+  * Arrays
+    * [Get Products of all other elements in Ruby](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/get_products_of_all_other_elements.rb)
   * Binary Trees
     * [Inorder Traversal](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/binary_trees/inorder_traversal.rb)
     * [Invert](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/binary_trees/invert.rb)

From dcfdf73a7f937e12470a585add4e6107ef942583 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sat, 19 Dec 2020 20:20:45 -0800
Subject: [PATCH 11/32] Separators

---
 data_structures/arrays/get_products_of_all_other_elements.rb | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/data_structures/arrays/get_products_of_all_other_elements.rb b/data_structures/arrays/get_products_of_all_other_elements.rb
index b4a8a2f..e22dd1a 100644
--- a/data_structures/arrays/get_products_of_all_other_elements.rb
+++ b/data_structures/arrays/get_products_of_all_other_elements.rb
@@ -5,7 +5,9 @@
 # each element at index `i` of the new array is the product of
 # all the numbers in the original array except the one at `i`.
 
+#
 # 1. Brute force solution
+# 
 def calculate_products_of_all_other_elements(nums)
   products_other_elements = Array.new(nums.length, 1)
 
@@ -22,8 +24,10 @@ end
 
 puts(calculate_products_of_all_other_elements([1, 2, 3]))
 
+#
 # 2. O(n) time and space
 # Arrays - Get Products of all other elements in Ruby
+#
 
 # Generates prefix products
 def build_prefix_products(nums)

From a285989e1cf2601c519bd338aab2d8b115b879b6 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sat, 19 Dec 2020 20:23:48 -0800
Subject: [PATCH 12/32] Rename var

---
 .../arrays/get_products_of_all_other_elements.rb          | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/data_structures/arrays/get_products_of_all_other_elements.rb b/data_structures/arrays/get_products_of_all_other_elements.rb
index e22dd1a..0e7d97d 100644
--- a/data_structures/arrays/get_products_of_all_other_elements.rb
+++ b/data_structures/arrays/get_products_of_all_other_elements.rb
@@ -7,19 +7,19 @@
 
 #
 # 1. Brute force solution
-# 
+#
 def calculate_products_of_all_other_elements(nums)
-  products_other_elements = Array.new(nums.length, 1)
+  product_of_other_elements = Array.new(nums.length, 1)
 
   nums.each_with_index do |num1, i|
     nums.each_with_index do |num2, j|
       if (i != j)
-        products_other_elements[i] = products_other_elements[i] * num2
+        product_of_other_elements[i] = product_of_other_elements[i] * num2
       end
     end
   end
 
-  products_other_elements
+  product_of_other_elements
 end
 
 puts(calculate_products_of_all_other_elements([1, 2, 3]))

From 6a64ce0c5ac381f79a7243b62341e90a05a0e7ca Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sat, 19 Dec 2020 20:24:18 -0800
Subject: [PATCH 13/32] Update DIRECTORY.md

---
 DIRECTORY.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index e2a7845..d0f0b0a 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -4,7 +4,7 @@
 
 ## Data Structures
   * Arrays
-    * [Get Products of all other elements in Ruby](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/get_products_of_all_other_elements.rb)
+    * [Get products of all other elements in Ruby](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/get_products_of_all_other_elements.rb)
   * Binary Trees
     * [Inorder Traversal](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/binary_trees/inorder_traversal.rb)
     * [Invert](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/binary_trees/invert.rb)

From 4586b9dcd91c78f7a8dc56c8d0b58f74c0abad7e Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 20 Dec 2020 16:06:24 -0800
Subject: [PATCH 14/32] Add Search algorithm: Recursive linear search

---
 searches/recursive_linear_search.rb | 30 +++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 searches/recursive_linear_search.rb

diff --git a/searches/recursive_linear_search.rb b/searches/recursive_linear_search.rb
new file mode 100644
index 0000000..67065cd
--- /dev/null
+++ b/searches/recursive_linear_search.rb
@@ -0,0 +1,30 @@
+=begin
+A pure Ruby implementation of a recursive linear search algorithm
+=end
+
+def rec_linear_search(sequence, low, high, target)
+    unless (high < sequence.length && low < sequence.length)
+      raise Exception("Invalid upper or lower bound!")
+    end
+
+    if high < low
+      return -1
+    end
+    if sequence[low] == target
+      return low
+    end
+    if sequence[high] == target
+      return high
+    end
+
+    return rec_linear_search(sequence, low + 1, high - 1, target)
+end
+
+puts(rec_linear_search([0, 30, 500, 100, 700], 0, 4, 0))
+# => 0
+puts(rec_linear_search([0, 30, 500, 100, 700], 0, 4, 700))
+# => 4
+puts(rec_linear_search([0, 30, 500, 100, 700], 0, 4, 30))
+# => 1
+puts(rec_linear_search([0, 30, 500, 100, 700], 0, 4, -6))
+# => -1

From c5898581f46a1309f80a3d42ee566e3688653d7d Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 20 Dec 2020 16:08:48 -0800
Subject: [PATCH 15/32] Fix rubocop offenses

---
 searches/recursive_linear_search.rb | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/searches/recursive_linear_search.rb b/searches/recursive_linear_search.rb
index 67065cd..0c80a8d 100644
--- a/searches/recursive_linear_search.rb
+++ b/searches/recursive_linear_search.rb
@@ -1,30 +1,25 @@
-=begin
-A pure Ruby implementation of a recursive linear search algorithm
-=end
+# A pure Ruby implementation of a recursive linear search algorithm
 
 def rec_linear_search(sequence, low, high, target)
-    unless (high < sequence.length && low < sequence.length)
-      raise Exception("Invalid upper or lower bound!")
-    end
+  raise Exception('Invalid upper or lower bound!') unless high < sequence.length && low < sequence.length
 
-    if high < low
-      return -1
-    end
-    if sequence[low] == target
-      return low
-    end
-    if sequence[high] == target
-      return high
-    end
+  return -1 if high < low
 
-    return rec_linear_search(sequence, low + 1, high - 1, target)
+  return low if sequence[low] == target
+
+  return high if sequence[high] == target
+
+  rec_linear_search(sequence, low + 1, high - 1, target)
 end
 
 puts(rec_linear_search([0, 30, 500, 100, 700], 0, 4, 0))
 # => 0
+
 puts(rec_linear_search([0, 30, 500, 100, 700], 0, 4, 700))
 # => 4
+
 puts(rec_linear_search([0, 30, 500, 100, 700], 0, 4, 30))
 # => 1
+
 puts(rec_linear_search([0, 30, 500, 100, 700], 0, 4, -6))
 # => -1

From 99fae7a9309a35434f56848b9b7e215feb9f407e Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 20 Dec 2020 16:11:46 -0800
Subject: [PATCH 16/32] Update DIRECTORY.md

---
 DIRECTORY.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 48513cb..27bfeaa 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -39,6 +39,7 @@
   * [Binary Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/binary_search.rb)
   * [Depth First Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/depth_first_search.rb)
   * [Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/linear_search.rb)
+  * [Recursive Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/recursive_linear_search.rb)
 
 ## Sorting
   * [Bogo Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bogo_sort.rb)

From 00a3e61cfec3cd817268634c8c9c53a0fc14d224 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 20 Dec 2020 16:49:22 -0800
Subject: [PATCH 17/32] Add double linear search

---
 searches/double_linear_search.rb | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)
 create mode 100644 searches/double_linear_search.rb

diff --git a/searches/double_linear_search.rb b/searches/double_linear_search.rb
new file mode 100644
index 0000000..e8b63f3
--- /dev/null
+++ b/searches/double_linear_search.rb
@@ -0,0 +1,29 @@
+# Iterate through the array from both sides to find the index of search_item.
+
+def double_linear_search(array, search_item)
+  start_ind = 0
+  end_ind = array.length - 1
+
+  while start_ind <= end_ind
+    if array[start_ind] == search_item
+      return start_ind
+    elsif array[end_ind] == search_item
+      return end_ind
+    else
+      start_ind += 1
+      end_ind -= 1
+    end
+  end
+
+  # returns -1 if search_item is not found in array
+  return -1
+end
+
+puts(double_linear_search([1, 5, 5, 10], 1))
+# => 0
+puts(double_linear_search([1, 5, 5, 10], 5))
+# => 1
+puts(double_linear_search([1, 5, 5, 10], 100))
+# => -1
+puts(double_linear_search([1, 5, 5, 10], 10))
+# => 3

From e2a03f33c4e7ef662ede4323b4f33a886404b8b2 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 20 Dec 2020 16:50:42 -0800
Subject: [PATCH 18/32] Pass rubocop

---
 searches/double_linear_search.rb | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/searches/double_linear_search.rb b/searches/double_linear_search.rb
index e8b63f3..e68b02f 100644
--- a/searches/double_linear_search.rb
+++ b/searches/double_linear_search.rb
@@ -5,18 +5,15 @@ def double_linear_search(array, search_item)
   end_ind = array.length - 1
 
   while start_ind <= end_ind
-    if array[start_ind] == search_item
-      return start_ind
-    elsif array[end_ind] == search_item
-      return end_ind
-    else
-      start_ind += 1
-      end_ind -= 1
-    end
+    return start_ind if array[start_ind] == search_item
+    return end_ind if array[end_ind] == search_item
+
+    start_ind += 1
+    end_ind -= 1
   end
 
   # returns -1 if search_item is not found in array
-  return -1
+  -1
 end
 
 puts(double_linear_search([1, 5, 5, 10], 1))

From 7afb2806d31fd0af962d06aa7906d0633870c825 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 20 Dec 2020 16:51:23 -0800
Subject: [PATCH 19/32] Update DIRECTORY.md

---
 DIRECTORY.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 48513cb..b668d4f 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -39,6 +39,7 @@
   * [Binary Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/binary_search.rb)
   * [Depth First Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/depth_first_search.rb)
   * [Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/linear_search.rb)
+  * [Double Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/double_linear_search.rb)
 
 ## Sorting
   * [Bogo Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bogo_sort.rb)

From 7289ef00552117c4e08131009475abedf5d7e944 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 20 Dec 2020 16:53:04 -0800
Subject: [PATCH 20/32] spaces

---
 searches/double_linear_search.rb | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/searches/double_linear_search.rb b/searches/double_linear_search.rb
index e68b02f..86abbfe 100644
--- a/searches/double_linear_search.rb
+++ b/searches/double_linear_search.rb
@@ -18,9 +18,12 @@ end
 
 puts(double_linear_search([1, 5, 5, 10], 1))
 # => 0
+
 puts(double_linear_search([1, 5, 5, 10], 5))
 # => 1
+
 puts(double_linear_search([1, 5, 5, 10], 100))
 # => -1
+
 puts(double_linear_search([1, 5, 5, 10], 10))
 # => 3

From 4de3238d39098d6df18e9119ca619a2355fb9421 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 20 Dec 2020 17:01:07 -0800
Subject: [PATCH 21/32] Add Recursive Double Linear Search

---
 searches/recursive_double_linear_search.rb | 28 ++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 searches/recursive_double_linear_search.rb

diff --git a/searches/recursive_double_linear_search.rb b/searches/recursive_double_linear_search.rb
new file mode 100644
index 0000000..f38f4a3
--- /dev/null
+++ b/searches/recursive_double_linear_search.rb
@@ -0,0 +1,28 @@
+# Iterate through the array to find the index of key using recursion.
+
+def recursive_double_linear_search(data, key, left = 0, right = 0)
+  right &&= data.length - 1
+
+  return -1 if left > right
+
+  return left if data[left] == key
+
+  return right if data[right] == key
+
+  recursive_double_linear_search(data, key, left + 1, right - 1)
+end
+
+puts(recursive_double_linear_search([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11], 5))
+# => 5
+
+puts(recursive_double_linear_search([1, 2, 4, 5, 3], 4))
+# => 2
+
+puts(recursive_double_linear_search([1, 2, 4, 5, 3], 6))
+# => -1
+
+puts(recursive_double_linear_search([5], 5))
+# => 0
+
+puts(recursive_double_linear_search([], 1))
+# => -1

From c82082c3c43881200eb7768fdb4815155a431795 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 20 Dec 2020 17:01:42 -0800
Subject: [PATCH 22/32] Add entry to DIRECTORY.md

---
 DIRECTORY.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 48513cb..4a879d0 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -39,6 +39,7 @@
   * [Binary Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/binary_search.rb)
   * [Depth First Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/depth_first_search.rb)
   * [Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/linear_search.rb)
+  * [Recursive Double Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/recursive_double_linear_search.rb)
 
 ## Sorting
   * [Bogo Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bogo_sort.rb)

From 89ad4fdbbc2f284a15f718ca9a606e625d4d22fb Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 20 Dec 2020 17:02:35 -0800
Subject: [PATCH 23/32] Kill spaces

---
 searches/recursive_double_linear_search.rb | 1 -
 1 file changed, 1 deletion(-)

diff --git a/searches/recursive_double_linear_search.rb b/searches/recursive_double_linear_search.rb
index f38f4a3..ade0f59 100644
--- a/searches/recursive_double_linear_search.rb
+++ b/searches/recursive_double_linear_search.rb
@@ -6,7 +6,6 @@ def recursive_double_linear_search(data, key, left = 0, right = 0)
   return -1 if left > right
 
   return left if data[left] == key
-
   return right if data[right] == key
 
   recursive_double_linear_search(data, key, left + 1, right - 1)

From 43ebe0c33edffaab11db21f7e8bfc1e9b7bc383a Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 27 Dec 2020 11:13:10 -0800
Subject: [PATCH 24/32] Add Trie data structure: Search string

---
 data_structures/tries/trie.rb | 75 +++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 data_structures/tries/trie.rb

diff --git a/data_structures/tries/trie.rb b/data_structures/tries/trie.rb
new file mode 100644
index 0000000..2a3cb2f
--- /dev/null
+++ b/data_structures/tries/trie.rb
@@ -0,0 +1,75 @@
+# A Trie (prefix tree) is a kind of search tree used to provide quick lookup
+# of words/patterns in a set of words. A basic Trie however has O(n^2)
+# space complexity making it impractical in practice.
+# It however provides O(max(search_string, length of longest word))
+# lookup time making it an optimal approach when space is not an issue.
+
+class Node
+  attr_reader   :value, :next
+  attr_accessor :word
+
+  def initialize(value)
+    @value = value
+    @word  = false
+    @next  = []
+  end
+end
+
+class Trie
+  def initialize
+    @root = Node.new('*')
+  end
+
+  def insert_many(word)
+    letters = word.chars
+    base    = @root
+
+    letters.each do |letter|
+      base = insert(letter, base.next)
+    end
+  end
+
+  def include?(word)
+    letters = word.chars
+    base    = @root
+
+    letters.all? do |letter|
+      base = find(letter, base.next)
+    end
+  end
+
+  private
+
+  # check if it already exists
+  # if not add character to node
+  def insert(character, trie)
+    found = trie.find do |n|
+      n.value == character
+    end
+
+    add_node(character, trie) unless found
+  end
+
+  def add_node(character, trie)
+    Node.new(character).tap do |new_node|
+      trie << new_node
+    end
+  end
+
+  def find(character, trie)
+    trie.find do |n|
+      n.value == character
+    end
+  end
+end
+
+trie = Trie.new
+trie.insert_many('Dogs')
+trie.insert_many('South')
+trie.insert_many('Cape Town')
+
+puts trie.include?('Cape Town')
+# => true
+
+puts trie.include?('not presented')
+# => false

From bfcba1016bcb51d7070184d40fc64458be112f5f Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sun, 27 Dec 2020 14:15:21 -0800
Subject: [PATCH 25/32] Update directory.md

---
 DIRECTORY.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 48513cb..7cbdff4 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -11,6 +11,8 @@
   * Linked Lists
     * [Double List](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/linked_lists/double_list.rb)
     * [Single List](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/linked_lists/single_list.rb)
+  * Tries
+    * [Trie](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/tries/trie.rb)
 
 ## Discrete Mathematics
   * [Euclidean Gcd](https://github.com/TheAlgorithms/Ruby/blob/master/discrete_mathematics/euclidean_gcd.rb)

From 40b463589524c7b3c7c167565eb3b38f2f509def Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Mon, 28 Dec 2020 09:00:19 -0800
Subject: [PATCH 26/32] Update DIRECTORY.md

---
 DIRECTORY.md | 1 -
 1 file changed, 1 deletion(-)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 2fcb289..48513cb 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -42,7 +42,6 @@
 
 ## Sorting
   * [Bogo Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bogo_sort.rb)
-  * [Bogo Sort Test](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bogo_sort_test.rb)
   * [Bubble Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bubble_sort.rb)
   * [Bucket Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bucket_sort.rb)
   * [Heap Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/heap_sort.rb)

From 082a02e7613545a63a253fc926e53129d3cb726b Mon Sep 17 00:00:00 2001
From: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Date: Mon, 28 Dec 2020 17:00:35 +0000
Subject: [PATCH 27/32] updating DIRECTORY.md

---
 DIRECTORY.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 48513cb..2fcb289 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -42,6 +42,7 @@
 
 ## Sorting
   * [Bogo Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bogo_sort.rb)
+  * [Bogo Sort Test](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bogo_sort_test.rb)
   * [Bubble Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bubble_sort.rb)
   * [Bucket Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bucket_sort.rb)
   * [Heap Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/heap_sort.rb)

From 90ac8a1a635a054392f3d355816c2372ddef2824 Mon Sep 17 00:00:00 2001
From: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Date: Mon, 28 Dec 2020 22:36:08 +0000
Subject: [PATCH 28/32] updating DIRECTORY.md

---
 DIRECTORY.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 2fcb289..6824cfd 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -19,6 +19,10 @@
 ## Other
   * [Fisher Yates](https://github.com/TheAlgorithms/Ruby/blob/master/other/fisher_yates.rb)
 
+## Project Euler
+  * Problem 4
+    * [Problem4 Sol1](https://github.com/TheAlgorithms/Ruby/blob/master/Project%20Euler/Problem%204/problem4_sol1.rb)
+
 ## Project Euler
   * Problem 1
     * [Problem1 Sol1](https://github.com/TheAlgorithms/Ruby/blob/master/project_euler/problem_1/problem1_sol1.rb)

From 46761fb6be7de8098d548a749a6a90842bebab59 Mon Sep 17 00:00:00 2001
From: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Date: Mon, 28 Dec 2020 22:37:02 +0000
Subject: [PATCH 29/32] updating DIRECTORY.md

---
 DIRECTORY.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 6824cfd..cd07ffa 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -20,6 +20,8 @@
   * [Fisher Yates](https://github.com/TheAlgorithms/Ruby/blob/master/other/fisher_yates.rb)
 
 ## Project Euler
+  * Problem 3
+    * [Problem3 Sol1](https://github.com/TheAlgorithms/Ruby/blob/master/Project%20Euler/Problem%203/problem3_sol1.rb)
   * Problem 4
     * [Problem4 Sol1](https://github.com/TheAlgorithms/Ruby/blob/master/Project%20Euler/Problem%204/problem4_sol1.rb)
 

From 610d9deab3040187a0c8afd0536579b95d738ae2 Mon Sep 17 00:00:00 2001
From: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Date: Mon, 28 Dec 2020 22:37:24 +0000
Subject: [PATCH 30/32] updating DIRECTORY.md

---
 DIRECTORY.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 1fb6494..ed7e774 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -4,7 +4,7 @@
 
 ## Data Structures
   * Arrays
-    * [Get products of all other elements in Ruby](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/get_products_of_all_other_elements.rb)
+    * [Get Products Of All Other Elements](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/get_products_of_all_other_elements.rb)
   * Binary Trees
     * [Inorder Traversal](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/binary_trees/inorder_traversal.rb)
     * [Invert](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/binary_trees/invert.rb)

From 529f715f7a3883f8ebfc8ad078b6cc8445ca966a Mon Sep 17 00:00:00 2001
From: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Date: Mon, 28 Dec 2020 22:38:25 +0000
Subject: [PATCH 31/32] updating DIRECTORY.md

---
 DIRECTORY.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 35c593e..dc8778a 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -46,8 +46,8 @@
 ## Searches
   * [Binary Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/binary_search.rb)
   * [Depth First Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/depth_first_search.rb)
-  * [Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/linear_search.rb)
   * [Double Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/double_linear_search.rb)
+  * [Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/linear_search.rb)
   * [Recursive Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/recursive_linear_search.rb)
 
 ## Sorting

From 2eea7df79766be736309fd423100927a4c53c353 Mon Sep 17 00:00:00 2001
From: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Date: Mon, 28 Dec 2020 22:39:16 +0000
Subject: [PATCH 32/32] updating DIRECTORY.md

---
 DIRECTORY.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 9dae632..9fc5c68 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -46,10 +46,10 @@
 ## Searches
   * [Binary Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/binary_search.rb)
   * [Depth First Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/depth_first_search.rb)
-  * [Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/linear_search.rb)
-  * [Recursive Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/recursive_linear_search.rb)
   * [Double Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/double_linear_search.rb)
+  * [Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/linear_search.rb)
   * [Recursive Double Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/recursive_double_linear_search.rb)
+  * [Recursive Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/recursive_linear_search.rb)
 
 ## Sorting
   * [Bogo Sort](https://github.com/TheAlgorithms/Ruby/blob/master/sorting/bogo_sort.rb)