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require 'enumerator'
module Hashery
# LinkedList implements a simple doubly linked list with efficient
# hash-like element access.
#
# This is a simple linked-list implementation with efficient random
# access of data elements. It was inspired by George Moscovitis'
# LRUCache implementation found in Facets 1.7.30, but unlike the
# linked-list in that cache, this one does not require the use of a
# mixin on any class to be stored. The linked-list provides the
# push, pop, shift, unshift, first, last, delete and length methods
# which work just like their namesakes in the Array class, but it
# also supports setting and retrieving values by key, just like a
# hash.
#
# LinkedList was ported from the original in Kirk Hanes IOWA web framework.
#
# == Acknowledgements
#
# LinkedList is based on the LinkedList library by Kirk Haines.
#
# Copyright (C) 2006 Kirk Haines <khaines@enigo.com>.
#
class LinkedList
include Enumerable
# Represents a single node of the linked list.
#
class Node
attr_accessor :key, :value, :prev_node, :next_node
def initialize(key=nil,value=nil,prev_node=nil,next_node=nil)
@key = key
@value = value
@prev_node = prev_node
@next_node = next_node
end
end
#
# Initialize new LinkedList instance.
#
def initialize
@head = Node.new
@tail = Node.new
@lookup = Hash.new
node_join(@head,@tail)
end
#
# Lookup entry by key.
#
def [](key)
@lookup[key].value
end
#
# Add node to linked list.
#
def []=(k,v)
if @lookup.has_key?(k)
@lookup[k].value = v
else
n = Node.new(k,v,@head,@head.next_node)
node_join(n,@head.next_node)
node_join(@head,n)
@lookup[k] = n
end
v
end
#
# Is linked list empty?
#
def empty?
@lookup.empty?
end
#
# Remove node idenified by key.
#
def delete(key)
n = @lookup.delete(key)
v = n ? node_purge(n) : nil
v
end
#
# Get value of first node.
#
def first
@head.next_node.value
end
#
# Get value of last node.
#
def last
@tail.prev_node.value
end
#
#
#
def shift
k = @head.next_node.key
n = @lookup.delete(k)
node_delete(n) if n
end
#
#
#
def unshift(v)
if @lookup.has_key?(v)
n = @lookup[v]
node_delete(n)
node_join(n,@head.next_node)
node_join(@head,n)
else
n = Node.new(v,v,@head,@head.next_node)
node_join(n,@head.next_node)
node_join(@head,n)
@lookup[v] = n
end
v
end
#
#
#
def pop
k = @tail.prev_node.key
n = @lookup.delete(k)
node_delete(n) if n
end
#
#
#
def push(v)
if @lookup.has_key?(v)
n = @lookup[v]
node_delete(n)
node_join(@tail.prev_node,n)
node_join(n,@tail)
else
n = Node.new(v,v,@tail.prev_node,@tail)
node_join(@tail.prev_node,n)
node_join(n,@tail)
@lookup[v] = n
end
v
end
alias :<< :push
#
# Produces an Array of key values.
#
# Returns [Array].
#
def queue
r = []
n = @head
while (n = n.next_node) and n != @tail
r << n.key
end
r
end
#
# Converts to an Array of node values.
#
# Returns [Array].
#
def to_a
r = []
n = @head
while (n = n.next_node) and n != @tail
r << n.value
end
r
end
#
# Number of nodes.
#
def length
@lookup.length
end
alias size length
#
# Iterate over nodes, starting with the head node
# and ending with the tail node.
#
def each
n = @head
while (n = n.next_node) and n != @tail
yield(n.key,n.value)
end
end
private
#
# Delete a node.
#
# n - A node.
#
def node_delete(n)
node_join(n.prev_node,n.next_node)
v = n.value
end
#
# Purge a node.
#
# n - A node.
#
def node_purge(n)
node_join(n.prev_node,n.next_node)
v = n.value
n.value = nil
n.key = nil
n.next_node = nil
n.prev_node = nil
v
end
# Join two nodes.
#
# a - A node.
# b - A node.
#
def node_join(a,b)
a.next_node = b
b.prev_node = a
end
end
end
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