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