cloneGraph.rb

# Definition for a Node.
# class Node
#     attr_accessor :val, :neighbors
#     def initialize(val = 0, neighbors = nil)
#		  @val = val
#		  neighbors = [] if neighbors.nil?
#         @neighbors = neighbors
#     end
# end

# @param {Node} node
# @return {Node}
def cloneGraph(node)
   _cloneGraph(node, {}) 
end

def _cloneGraph(node, memo)
    return nil if node.nil?
    return memo[node.val] if memo.include? node.val

    new_node = memo[node.val] = Node.new node.val
    new_node.neighbors = node.neighbors.map { |n| _cloneGraph(n, memo) }
    
    new_node
end