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trie.py
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trie.py
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'''An implementation of the Trie data structure, which enables efficient
searches for strings based on substrings that begin them.
See https://en.wikipedia.org/wiki/Trie.
'''
import unittest
import pprint
class Trie:
'''An implementation of tries, based on a tree mapping values to dicts.'''
def __init__(self, words=None):
self.tree = {}
if not words:
return
self.add_all(words)
def add(self, word, **kwargs):
assert isinstance(word, str), 'only strings allowed in Trie'
if 'child' not in kwargs:
child = self.tree
else:
child = kwargs['child']
if not word:
child[''] = {}
return
child.setdefault(word[0], {})
self.add(word[1:], child = child[word[0]])
def add_all(self, words):
for word in words:
self.add(word)
def remove(self, word: str) -> bool:
"""Eagerly remove the word from the trie rooted at `root`.
Return whether the trie rooted at `root` is now empty.
THIS METHOD IS SLIGHTLY MODIFIED FROM THE delete() METHOD IN THE WIKIPEDIA
ARTICLE https://en.wikipedia.org/wiki/Trie.
"""
def _delete(child: dict, word: str, d: int) -> bool:
"""Clear the node corresponding to word[d], and delete the child word[d+1]
if that subtrie is completely empty, and return whether `node` has been
cleared.
"""
if d == len(word):
try:
del child['']
except:
raise KeyError(f"{repr(word)} is not in this Trie")
else:
c = word[d]
try:
if _delete(child[c], word, d+1):
del child[c]
except:
raise KeyError(f"{repr(word)} is not in this Trie.")
# Return whether the subtrie rooted at `node` is now completely empty
return len(child) == 0
return _delete(self.tree, word, 0)
def __contains__(self, word, **kwargs):
if 'child' not in kwargs:
child = self.tree
else:
child = kwargs['child']
if not word:
if '' in child:
return True
return False
if word[0] in child:
return self.__contains__(word[1:], child = child[word[0]])
def super_words(self, word, **kwargs):
if 'curword' not in kwargs:
curword = ''
else:
curword = kwargs['curword']
if 'child' not in kwargs:
child = self.tree
else:
child = kwargs['child']
if word == '':
for val in child:
if val == '':
yield curword
yield from self.super_words('',
curword = curword + val,
child = child[val])
return
if word[0] in child:
yield from self.super_words(word[1:],
curword = curword + word[0],
child = child[word[0]])
return
def __str__(self):
return f"Trie({pprint.pformat(self.tree, width = 40)})"
class TrieTester(unittest.TestCase):
def test_add_contains(self):
t = Trie()
t.add('ab')
self.assertIn('ab', t)
def test_remove(self):
t = Trie()
t.add('ab')
t.remove('ab')
self.assertNotIn('ab', t)
def test_remove_not_in_t(self):
t = Trie()
with self.assertRaisesRegex(KeyError, "not in this Trie"):
t.remove('ab')
def test_substring_not_in_t(self):
t = Trie()
t.add('aba')
with self.assertRaisesRegex(KeyError, "not in this Trie"):
t.remove('ab')
def test_remove_substring(self):
t = Trie()
t.add('aba')
t.add('ab')
t.remove('ab')
self.assertIn('aba', t)
def test_remove_superstring(self):
t = Trie()
t.add('aba')
t.add('ab')
t.remove('aba')
self.assertIn('ab', t)
def test_remove_unrelated_string(self):
t = Trie()
t.add('a')
t.add('b')
t.remove('b')
self.assertIn('a', t)
def test_empty_string(self):
t = Trie()
t.add('')
self.assertIn('', t)
def test_remove_empty_string(self):
t = Trie()
t.add('')
t.add('ab')
t.remove('')
self.assertNotIn('', t)
self.assertIn('ab', t)
def test_super_words_none(self):
t = Trie()
t.add('a')
self.assertEqual(list(t.super_words('b')), [])
def test_super_words_word_in_t_one_result(self):
t = Trie()
t.add('ab')
self.assertEqual(list(t.super_words('ab')), ['ab'])
def test_super_words_word_not_in_t_one_result(self):
t = Trie()
t.add('ab')
self.assertEqual(list(t.super_words('a')), ['ab'])
def test_super_words_word_in_t_multi_results(self):
t = Trie()
t.add('dog')
t.add('dogged')
t.add('abacus')
self.assertEqual(set(t.super_words('dog')), {'dog', 'dogged'})
def test_super_words_word_not_in_t_multi_results(self):
t = Trie()
t.add('dog')
t.add('abeyance')
t.add('abacus')
self.assertEqual(set(t.super_words('ab')), {'abacus', 'abeyance'})
def test_init_with_list(self):
t = Trie(['a', 'ab'])
self.assertEqual(set(t.super_words('')), {'a', 'ab'})
if __name__ == '__main__':
unittest.main()