Merge pull request #69 from vbrazo/add-trie-data-structure-example

Trie data structure: Search string

DIRECTORY.md

@@ -13,6 +13,8 @@
   * 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)

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