Class: Classbench::Trie

Inherits:
Object
  • Object
show all
Defined in:
lib/classbench/trie.rb

Overview

Class for representation of a n-ary prefix tree - trie.

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Trie

Returns a new instance of Trie.



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# File 'lib/classbench/trie.rb', line 77

def initialize
end

Instance Attribute Details

#root ⇒ Object

Returns the value of attribute root.



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# File 'lib/classbench/trie.rb', line 75

def root
  @root
end

Class Method Details

.get_prefix_nesting(node) ⇒ Object 



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# File 'lib/classbench/trie.rb', line 107

def self.get_prefix_nesting(node)
  if node # non-empty subtree
     # get prefix nesting from successor nodes
     zero_nesting = get_prefix_nesting(node.subtree["0"])
     one_nesting = get_prefix_nesting(node.subtree["1"])
     # will this node increase prefix nesting?
     if node.prefixes_count > 0 # this is a prefix node
      is_prefix = 1
     else
      is_prefix = 0
     end

     # return maximum of successors' nesting, possibly incremented
     if zero_nesting > one_nesting
      return zero_nesting + is_prefix
     else
      return one_nesting + is_prefix
     end
  else # empty subtree
     return 0
  end
end

Instance Method Details

#get_stats ⇒ Object

Erase not implemented/neccessary



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# File 'lib/classbench/trie.rb', line 132

def get_stats
  stats = TrieStats.new

  return stats if not root
  root.compute_weights

  level = root.level

  que = [root]
  # BFS, append from right, take from left
  while not que.empty?
    node = que.shift # take one from left

    node.subtree.each do |char, subnode|
      que << subnode
    end

    # level change - finish statistics computation for the previous level
    if node.level != level
      # auxiliary variables
      one_child = stats.nodes.one_child[level];
      two_children = stats.nodes.two_children[level];
      sum = one_child + two_children;
      # branching_one_child and branching_two_children
      if sum != 0
        stats.classbench.branching_one_child[level] =
          one_child.to_f / sum;
        stats.classbench.branching_two_children[level] =
          two_children.to_f / sum;
      end
      # skew
      if two_children != 0
        stats.classbench.skew[level] /= two_children.to_f;
      end
      # increment the level counter
      level += 1;
    end

    # trie node visit - classbench statistics
    stats.classbench.prefix_lengths[level] += node.prefixes_count;
    if node.subtree["0"] and node.subtree["1"] # skew is defined
      if node.zero_weight > node.one_weight # lighter 1-subtree
        skew = 1 - (node.one_weight.to_f / node.zero_weight);
      else # lighter 0-subtree
        skew = 1 - (node.zero_weight.to_f / node.one_weight);
      end
      stats.classbench.skew[level] += skew;
    end

    # trie node visit - nodes statistics
    if node.subtree["0"].nil?
      if node.subtree["1"].nil? # leaf node
        stats.nodes.leaf[level] += 1
      else # one child node
        stats.nodes.one_child[level] += 1
      end
    else # node->zero != NULL
      if node.subtree["1"] # two child node
        stats.nodes.two_children[level] += 1
      else # one child node
        stats.nodes.one_child[level] += 1
      end
    end

    if node.prefixes_count > 0 # prefix node
      stats.nodes.prefix[level] += 1
    else # non-prefix node
      stats.nodes.non_prefix[level] += 1
    end

  end # end of while BFS

  # finish statistics computation for the last level
  # auxiliary variables
  one_child = stats.nodes.one_child[level]
  two_children = stats.nodes.two_children[level]
  sum = one_child + two_children
  # branching_one_child and branching_two_children
  if sum != 0
    stats.classbench.branching_one_child[level] =
      one_child.to_f / sum
    stats.classbench.branching_two_children[level] =
      two_children.to_f / sum
  end
  # skew
  if two_children != 0
    stats.classbench.skew[level] /= two_children.to_f
  end
  # compute prefix nesting
  stats.classbench.prefix_nesting = Trie.get_prefix_nesting(root)

  return stats
end

#insert(prefix) ⇒ Object 



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# File 'lib/classbench/trie.rb', line 80

def insert(prefix)
  self.root = TrieNode.new(0) if not root

  # Empty prefix
  if prefix.size == 0
    root.increment_prefixes
    return
  end

  current_node = self.root
  next_node = nil

  # For each char
  prefix.split('').each_with_index do |ch, i|
    next_node = current_node.subtree[ch]

    if next_node.nil?
      next_node = TrieNode.new(i+1)
      current_node.subtree[ch] = next_node
    end

    current_node = next_node
  end

  current_node.increment_prefixes
end