Merge branch 'master' into add-stack-data-structure-example

.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

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](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)
@@ -13,7 +15,8 @@
     * [Single List](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/linked_lists/single_list.rb)
   * Stacks
     * [Stack](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/stacks/stack.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)
@@ -22,6 +25,12 @@
 ## Other
   * [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)
+
 ## Project Euler
   * Problem 1
     * [Problem1 Sol1](https://github.com/TheAlgorithms/Ruby/blob/master/project_euler/problem_1/problem1_sol1.rb)
@@ -41,10 +50,14 @@
 ## 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)
+  * [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)
+  * [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)

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)
+

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

Rakefile

@@ -0,0 +1,7 @@
+require 'rake/testtask'
+
+Rake::TestTask.new(:test) do |t|
+  t.test_files = FileList['**/*_test.rb']
+end
+
+task default: :test

data_structures/arrays/get_products_of_all_other_elements.rb

@@ -0,0 +1,89 @@
+# 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)
+  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)
+        product_of_other_elements[i] = product_of_other_elements[i] * num2
+      end
+    end
+  end
+
+  product_of_other_elements
+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]

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

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
+    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
+  -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

searches/recursive_double_linear_search.rb

@@ -0,0 +1,27 @@
+# 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

searches/recursive_linear_search.rb

@@ -0,0 +1,25 @@
+# A pure Ruby implementation of a recursive linear search algorithm
+
+def rec_linear_search(sequence, low, high, target)
+  raise Exception('Invalid upper or lower bound!') unless high < sequence.length && low < sequence.length
+
+  return -1 if high < low
+
+  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

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

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