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