children_iterative.rb

def find_descendants(person)
  descendants = []
  stack = person[:children]

  until stack.empty?
    current_node = stack.pop

    children = current_node[:children]
    if children
      children.each do |child|
        stack.push child
      end
    end

    descendants << current_node
  end

  descendants
end


person = {
    name: 'Leo',
    children: [
        {name: 'Harvey', children: [
            {name: 'Kallin'},
            {name: 'Seth'}
        ]},
        {name: 'Paul', children: [
            {name: 'Mark'},
            {name: 'Alan'}
        ]},
    ]
}

puts find_descendants(person)