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] 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