Class: Trie

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

Overview

Trie

Description

Implementation of a trie data structure, well-suited for storing and looking up strings or other sequences.

More specifically, this is an implementation of a Patricia trie (en.wikipedia.org/wiki/Patricia_trie).

Usage

require "trie"

# Create a new Trie and insert some values into it.
t = Trie.new
t.insert("the", 1)
t.insert("they", 2)
t.insert("they", 3)
t.insert("their", 4).insert("they're", 5)

# Search for an exact match of "they".
t.find("they").values  # => [2, 3]

# Search for a prefix that will match all keys.
t2 = t.find_prefix("th")
puts t2.size  # prints 5

# In the sub-Trie beginning with "th", search for the prefix "ey"
# (therefore, getting the three values with keys beginning with "they").
t2.find_prefix("ey").each_value {|v| puts v }  # prints 2, 3, and 5

# Now search for "at" in the sub-Trie, which results in an empty Trie
# (as there are no keys beginning with "that").
puts t2.find_prefix("at").empty?  # prints true

# Delete all values keyed by "they" (note that this must be performed on
# the root Trie rather than the one returned by Trie.find_prefix -- read
# the "Notes" section to find out why).
t.delete("they")

Notes

Keys are stored internally as Arrays. If you use Strings as keys they will be automatically converted, and when you use a method to access them later you’ll receive them as Arrays instead. For example:

t = Trie.new.insert("abc", 1).insert("def", 2)
t.keys                        # => [["a", "b", "c"], ["d", "e", "f"]]
t.keys.collect {|k| k.join }  # => ["abc", "def"]

(I’m hesitant to add code that will return keys as Strings if the user has only passed in Strings so far.)

Empty nodes are compressed. The strings “row” and “ruby”, which would normally be stored as

     ''
     /
    r
   / \ 
  o   u
 /     \ 
w       b
         \ 
          y

are actually stored as

    ''
    /
   r
  / \ 
ow  uby

Because of this implementation (and to allow Trie.find to be called on nodes returned by Trie.find that contain compressed elements), Trie.find and Trie.find_prefix will in some (most) cases return Trie objects that are not members of the root Trie. As a result, methods such as Trie.insert, Trie.delete, and Trie.clear should only be called on Trie objects that were directly returned by Trie.new.

Instance Method Summary collapse

Constructor Details

#initializeTrie

Create a new empty Trie.

Example

t = Trie.new  # gasp!


113
114
115
116
117
118
# File 'lib/trie.rb', line 113

def initialize
  @values = Set.new
  @children = {}
  @compressed_key = []
  @compressed_values = Set.new
end

Instance Method Details

#[](key) ⇒ Object

Return all of the items matching a key.

Example

t = Trie.new.insert("a", 3).insert("a", 4).insert("b", 5)
t["a"]  # => [3, 4]


127
128
129
# File 'lib/trie.rb', line 127

def [](key)
  find(key).values
end

#clearObject

Clear the trie.

Example

t = Trie.new.insert("blah", 3).insert("a", 1)
t.clear  # t now contains no values


138
139
140
141
142
143
144
# File 'lib/trie.rb', line 138

def clear
  @values.clear
  @children.clear
  @compressed_key.clear
  @compressed_values.clear
  self
end

#delete(key) ⇒ Object

Delete all values with a given key.

Example

t = Trie.new.insert("a", 1).insert("a", 2).insert("abc", 3)
t.delete("a")  # t now only contains the third value


153
154
155
156
157
158
159
160
161
162
163
164
165
# File 'lib/trie.rb', line 153

def delete(key)
  key = key.split('') if key.is_a?(String)
  if key.empty?
    @values.clear
  elsif key == @compressed_key
    @compressed_key.clear
    @compressed_values.clear
  elsif @children[key[0]]
    @children[key[0]].delete(key[1..-1])
    @children.delete(key[0]) if @children[key[0]].empty?
  end
  self
end

#delete_pair(key, value) ⇒ Object

Delete a (key, value) pair.

Example

t = Trie.new.insert("a", 1).insert("a", 2)
t.delete_pair("a", 1)  # t now only contains the second value


192
193
194
195
196
197
198
199
200
201
202
203
204
# File 'lib/trie.rb', line 192

def delete_pair(key, value)
  key = key.split('') if key.is_a?(String)
  if key.empty?
    @values.delete(value)
  elsif key == @compressed_key
    @compressed_values.delete(value)
    @compressed_key.clear
  elsif @children[key[0]]
    @children[key[0]].delete_pair(key[1..-1], value)
    @children.delete(key[0]) if @children[key[0]].empty?
  end
  self
end

#delete_prefix(prefix) ⇒ Object

Delete all values keyed by a given prefix.

Example

t = Trie.new.insert("a", 1).insert("al", 2).insert("algernon", 3)
t.delete_prefix("al")  # t now only contains the first value


213
214
215
216
217
218
219
220
221
222
# File 'lib/trie.rb', line 213

def delete_prefix(prefix)
  prefix = prefix.split('') if prefix.is_a?(String)
  if prefix.empty? or prefix == @compressed_key[0...prefix.size]
    clear
  elsif @children[prefix[0]]
    @children[prefix[0]].delete_prefix(prefix[1..-1])
    @children.delete(prefix[0]) if @children[prefix[0]].empty?
  end
  self
end

#delete_value(value) ⇒ Object

Delete all occurences of an value.

Example

t = Trie.new.insert("a", 1).insert("blah", 1).insert("a", 2)
t.delete_value(1)  # t now only contains the third value


174
175
176
177
178
179
180
181
182
183
# File 'lib/trie.rb', line 174

def delete_value(value)
  @compressed_values.delete(value)
  @compressed_key.clear if @compressed_values.empty?
  @values.delete(value)
  @children.each do |p, t|
    t.delete_value(value)
    @children.delete(p) if t.empty?
  end
  self
end

#each(prefix = []) ⇒ Object

Calls block once for each (key, value) pair in the Trie, passing the the key and value as parameters.

Example

t = Trie.new.insert("a", 1).insert("b", 2)
t.each {|k, v| puts "#{k.join()}: #{v} }  # prints "a: 1" and "b: 2"


232
233
234
235
236
237
238
239
# File 'lib/trie.rb', line 232

def each(prefix=[])
  @values.each {|v| yield(prefix, v) }
  @compressed_values.each {|v| yield(prefix.dup.concat(@compressed_key), v) }
  @children.each do |k, t|
    t.each(prefix.dup.push(k)) {|key, value| yield(key, value) }
  end
  self
end

#each_key(prefix = []) {|prefix| ... } ⇒ Object

Calls block once for each key in the Trie, passing the key as a parameter.

Example

t = Trie.new.insert("abc", 1).insert("def", 2)
t.each_key {|key| puts key.join() }  # prints "abc" and "def"

Yields:

  • (prefix)


249
250
251
252
253
254
255
256
# File 'lib/trie.rb', line 249

def each_key(prefix=[])
  yield prefix if not @values.empty?
  yield prefix.dup.concat(@compressed_key) if not @compressed_values.empty?
  @children.each do |k, t|
    t.each_key(prefix.dup.push(k)) {|key| yield key }
  end
  self
end

#each_valueObject

Calls block once for each (key, value) pair in the Trie, passing the value as a parameter.

Example

t = Trie.new.insert("a", 1).insert("b", 2)
t.each_value {|value| puts value }  # prints "1" and "2"


266
267
268
269
270
271
# File 'lib/trie.rb', line 266

def each_value
  @compressed_values.each {|value| yield value }
  @values.each {|value| yield value }
  @children.each_value {|t| t.each_value {|value| yield value } }
  self
end

#empty?Boolean

Does this Trie contain no values?

Example

t = Trie.new
t.empty?  # => true
t.insert("blah", 1)
t.empty?  # => false

Returns:

  • (Boolean)


282
283
284
# File 'lib/trie.rb', line 282

def empty?
  size == 0
end

#find(key) ⇒ Object

Get a new Trie object containing all values with the passed-in key.

Example

t = Trie.new.insert("the", 1).insert("their", 2).insert("foo", 4)
t.find("the")  # => Trie containing the only first value


293
294
295
296
297
298
299
300
301
302
303
304
305
# File 'lib/trie.rb', line 293

def find(key)
  key = key.split('') if key.is_a?(String)
  if (key.empty? and @compressed_key.empty?) or key == @compressed_key
    trie = Trie.new
    @values.each {|v| trie.insert([], v) }
    @compressed_values.each {|v| trie.insert([], v) }
    trie
  elsif @children[key[0]]
    @children[key[0]].find(key[1..-1])
  else
    Trie.new
  end
end

#find_prefix(prefix) ⇒ Object

Get a new Trie object containing all values with keys that begin with the passed-in prefix.

Example

# Both calls return a Trie containing only the first value:
t = Trie.new.insert("test", 1).insert("testing", 2)
t.find_prefix("test")
t.find_prefix("").find("t").find("es").find("t").find("")


317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
# File 'lib/trie.rb', line 317

def find_prefix(prefix)
  prefix = prefix.split('') if prefix.is_a?(String)
  if prefix.empty?
    self
  elsif prefix == @compressed_key[0...prefix.size]
    trie = Trie.new
    @compressed_values.each do |value|
      trie.insert(@compressed_key[prefix.size..-1], value)
    end
    trie
  elsif @children[prefix[0]]
    @children[prefix[0]].find_prefix(prefix[1..-1])
  else
    Trie.new
  end
end

#insert(key, value) ⇒ Object

Insert an value into this Trie, keyed by the passed-in key, which can be any sort of indexable object.

Example

t = Trie.new.insert("this is a string of considerable length", [ 0, 4, ])
t.insert([ "abc", "def", ], "testing")


342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
# File 'lib/trie.rb', line 342

def insert(key, value)
  key = key.split('') if key.is_a?(String)
  if key != @compressed_key
    @compressed_values.each {|v| insert_in_child(@compressed_key, v) }
    @compressed_values.clear
    @compressed_key.clear
  end

  if key.empty?
    @values.add(value)
  elsif (@values.empty? and @children.empty?) or key == @compressed_key
    @compressed_key = key.dup
    @compressed_values.add(value)
  else
    insert_in_child(key, value)
  end
  self
end

#keysObject

Get an Array containing all keys in this Trie.

Example

t = Trie.new.insert("test", 1).insert([0, 1], 2)
t.keys  # => [['t', 'e', 's', 't'], [0, 1]]


378
379
380
381
382
# File 'lib/trie.rb', line 378

def keys
  a = []
  each_key {|key| a.push(key) }
  a
end

#num_nodesObject

Get the number of nodes used to represent this Trie.

This is only useful for testing.



389
390
391
392
393
# File 'lib/trie.rb', line 389

def num_nodes
  node_count = 1
  @children.each {|p, t| node_count += t.num_nodes }
  node_count
end

#sizeObject

Get the number of values contained in this Trie.

Example

t = Trie.new.insert("test", 1).insert("foo", 2)
t.size  # => 2


402
403
404
405
406
# File 'lib/trie.rb', line 402

def size
  child_count = 0
  @children.each_value {|t| child_count += t.size }
  @compressed_values.size + @values.size + child_count
end

#valuesObject

Get an Array containing all values in this Trie.

Example

t = Trie.new.insert("a", 1).insert("b", 2)
t.values  # => Array containing both values
t.values.each {|value| puts value }  # prints "1" and "2"


416
417
418
419
420
# File 'lib/trie.rb', line 416

def values
  a = []
  each_value {|value| a.push(value) }
  a
end