Constructing a Ruby Binary Tree from String

Question

A bit of a newbie to computing science.

I have the basics for a binary tree in Ruby:

class Node
  attr_accessor :left, :right, :value
  def initialize(value)
    @value = value
  end
end

This works fine if I construct it manually, for example, if I want tom to be a child node of ben:

ben = Node.new('Ben')
tom = Node.new('Tom')

ben.left = tom

One of the challenges I need to figure out is how to construct a tree for inputted parent/child pairs. Here is an example input string:

peter tom
peter marie
marie john
tom oscar

My binary tree would look something like this:

    peter
      |
 tom     marie
  |        |
oscar     john

I am wondering if I can get some direction into converting multiple strings in the following format "[parent] [child]" into a binary tree.

Thanks :)

With a [parent] [child] format, how do you decide whether a child goes into left or right? Likewise, what happens if the input contains more than two child entries for a given parent? — Stefan
– Stefan, Commented Sep 5, 2016 at 14:20

nloveladyallen · Accepted Answer · 2016-09-05 16:20:26Z

2

Use a hash to store the data:

data = Hash.new { |h, k| h[k] = Node.new k }

while !(line = gets.strip).empty?
    parent, child = line.split.map { |value| data[value] }
    if !parent.left
        parent.left = child
    elsif !parent.right
        parent.right = child
    else
        raise "#{parent.value} already has both a left and right child"
    end
end

edited Sep 5, 2016 at 16:20

answered Sep 5, 2016 at 15:10

nloveladyallen

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3 Comments

Cary Swoveland Over a year ago

Nice solution, especially the way you've defined data. One small thing: you need something like while (line = gets.strip) != ''. As it is you'll never break out of the loop.

nloveladyallen Over a year ago

@CarySwoveland Fixed.

Allister Over a year ago

Awesome solution! Worked perfectly. Thanks

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