Class: Btree::Node

Inherits:
Object
  • Object
show all
Defined in:
lib/btree/node.rb

Instance Method Summary collapse

Constructor Details

#initialize(degree) ⇒ Node

Returns a new instance of Node.



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# File 'lib/btree/node.rb', line 14

def initialize(degree)
  @degree = degree
  @keys = []
  @children = []
end

Instance Method Details

#add_child(node) ⇒ Object 



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# File 'lib/btree/node.rb', line 33

def add_child(node)
  @children << node
end

#children ⇒ Object 



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# File 'lib/btree/node.rb', line 37

def children
  @children.dup.freeze
end

#dump(level = 0) ⇒ Object 



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# File 'lib/btree/node.rb', line 20

def dump(level = 0)
  @keys.each_with_index do |key, idx|
    puts "LEVEL: #{level} => #{key.first}: full? #{full?} leaf? #{leaf?} children: #{values.inspect}"
    if @children[idx]
       @children[idx].dump(level + 1)
    end
  end
  (@children[@keys.size..-1] || []).each do |c|
    c.dump(level+1)
  end
  nil
end

#full? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/btree/node.rb', line 49

def full?
  size >= 2 * @degree - 1
end

#insert(key, value) ⇒ Object 



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# File 'lib/btree/node.rb', line 105

def insert(key, value)
  # The slot the key would occupy is also the slot it would already occupy if
  # it were present, so locating it and rejecting a duplicate are one step.
  # Checked at every node on the way down, not just at the leaf: a key that a
  # split has promoted into an internal node would otherwise be descended
  # past and inserted a second time, hiding one copy in a subtree.
  i = key_index(key)
  raise "Duplicate key" if i < size && @keys[i].first == key

  if leaf?
    @keys.insert(i, [key, value])
  else
    if @children[i] && @children[i].full?
      split(i)
      # The split just promoted a key into this node, after the check above.
      raise "Duplicate key" if @keys[i].first == key
      i += 1 if key > @keys[i].first
    end
    @children[i].insert(key, value)
  end
end

#keys ⇒ Object 



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# File 'lib/btree/node.rb', line 41

def keys
  @keys.map(&:first).freeze
end

#leaf? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/btree/node.rb', line 53

def leaf?
  @children.length == 0
end

#size ⇒ Object 



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# File 'lib/btree/node.rb', line 57

def size
  @keys.size
end

#split(child_idx) ⇒ Object 



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# File 'lib/btree/node.rb', line 127

def split(child_idx)
  raise "Invalid child index #{child_idx} in split, num_children = #{@children.size}" if child_idx < 0 || child_idx >= @children.size
  #puts "SPLIT1: #{self.inspect}"
  splitee = @children[child_idx]
  y = Btree::Node.new(@degree)
  z = Btree::Node.new(@degree)
  (@degree-1).times do |j|
    z._keys[j] = splitee._keys[j+@degree]
    y._keys[j] = splitee._keys[j]
  end
  if !splitee.leaf?
    @degree.times do |j|
      z._children[j] = splitee._children[j+@degree]
      y._children[j] = splitee._children[j]
    end
  end
  mid_val = splitee._keys[@degree-1]
  #puts "SPLIT2: #{self.inspect}"
  (@keys.size).downto(child_idx) do |j|
    @children[j+1] = @children[j]
  end

  @children[child_idx+1] = z
  @children[child_idx] = y
  
  #puts "SPLIT3: #{self.inspect}"

  (@keys.size - 1).downto(child_idx) do |j|
    @keys[j+1] = @keys[j]
  end

  #puts "SPLIT4: #{self.inspect}"

  @keys[child_idx] = mid_val
  #puts "SPLIT5: #{self.inspect}"
end

#value_of(key) ⇒ Object 



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# File 'lib/btree/node.rb', line 90

def value_of(key)

  return values_of(key) if key.kind_of? Range

  i = key_index(key)

  if i < size && key == @keys[i].first
    return @keys[i].last
  elsif leaf?
    return nil
  else
    return @children[i].value_of(key)
  end
end

#values ⇒ Object 



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# File 'lib/btree/node.rb', line 45

def values
  @keys.map(&:last).freeze
end

#values_of(range) ⇒ Object

Values whose keys fall in the range, in key order. Subtrees that cannot contain an in-range key are never visited.



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# File 'lib/btree/node.rb', line 63

def values_of(range)

  result = Array.new
  lo = range.begin
  hi = range.end

  # Skip the keys, and the subtrees between them, that sort entirely below
  # the range.  When every key is below it, this lands on the rightmost
  # child, which may still hold in-range keys.
  i = lo ? key_index(lo) : 0

  result += @children[i].values_of(range) if !leaf? && @children[i]

  while i < size
    key = @keys[i].first
    # Everything from here on sorts above the range.
    break if hi && (range.exclude_end? ? key >= hi : key > hi)
    result << @keys[i].last if range.cover? key
    result += @children[i+1].values_of(range) if !leaf? && @children[i+1]
    i += 1
  end

  result

end