tree_depth.rb

def tree_depth tree
  # use recursion
  # have a look at Array#max
  # Hash#empty? might help, too
  
  # your implementation here
end

if __FILE__ == $0
  require 'rspec/autorun'
  
  describe 'binary tree depth' do
    let(:tree) { {lft:{lft:{lft:{},rgt:{}}},rgt:{lft:{},rgt:{rgt:{}}}} }
    let(:ltree) { {lft:{lft:{lft:{}}}} }
    let(:rtree) { {rgt:{rgt:{rgt:{}}}} }
    it { tree_depth(tree).should == 4 }
    it { tree_depth(ltree).should == 4 }
    it { tree_depth(rtree).should == 4 }
  end
end

z-tree-solution.rb

Here...
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v


def tree_depth tree
  return 0 if tree.nil?
  return 1 if tree.empty?
  1 + [tree_depth(tree[:lft]), tree_depth(tree[:rgt])].max
end

if __FILE__ == $0
  require 'rspec/autorun'
  
  describe 'binary tree depth' do
    let(:tree) { {lft:{lft:{lft:{},rgt:{}}},rgt:{lft:{},rgt:{rgt:{}}}} }
    let(:ltree) { {lft:{lft:{lft:{}}}} }
    let(:rtree) { {rgt:{rgt:{rgt:{}}}} }
    it { tree_depth(tree).should == 4 }
    it { tree_depth(ltree).should == 4 }
    it { tree_depth(rtree).should == 4 }
  end
end