https://leetcode.com/problems/add-and-search-word-data-structure-design/

211.rb

class WordDictionary
  def initialize
    @root = Node.new
  end

  def add_word(word)
    @root.add_word(word, 0)
  end

  def search(word)
    @root.search(word, 0)
  end

  class Node
    def add_word(word, idx)
      if word.size == idx
        @complete = true
        return
      end

      ch = word[idx]
      child = children[ch]
      unless child
        child = Node.new
        children[ch] = child
      end
      child.add_word(word, idx + 1)
    end

    def search(word, idx)
      return found? if word.size == idx

      ch = word[idx]
      if ch == '.'
        children.values.any? { |child| child.search(word, idx + 1) }
      else
        child = children[ch]
        !child.nil? && child.search(word, idx + 1)
      end
    end

    def children
      @children ||= {}
    end

    def found?
      !!@complete
    end
  end
end