binary_tree.rb

#!/usr/bin/env ruby
Node = Struct.new(:value, :left, :right)

def create_tree(nodes, root=nil, idx=0)
  if nodes.size > idx
    root = Node.new(nodes[idx])
    root.left = create_tree(nodes, root.left, 2 * idx + 1)
    root.right = create_tree(nodes, root.right, 2 * idx + 2)
  end

  return root
end

require 'minitest/autorun'

describe 'create_tree' do
  it "should create a binary tree from an array" do
    arr = [1, 2, 3, 4, 5, 6]
    root = create_tree(arr)
    root.value.must_equal(1)
    root.left.value.must_equal(2)
    root.right.value.must_equal(3)
    root.left.left.value.must_equal(4)
    root.left.right.value.must_equal(5)
    root.right.left.value.must_equal(6)
    assert_nil(root.right.right)
  end
end