# Source code for tryalgo.trie

```
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""\
trie - correcteur orthographique
jill-jênn vie et christoph dürr - 2014-2019
"""
# Don't write a Trie class otherwise you cannot represent leaves with None
# snip{
from string import ascii_letters # in Python 2 one would import letters
# pylint: disable=missing-docstring, too-few-public-methods
[docs]
class TrieNode:
def __init__(self): # each node will have
self.is_word = False # 52 children -
self.s = {c: None for c in ascii_letters} # most will remain empty
[docs]
def add(T, w, i=0): # Add a word to the trie
"""
:param T: trie
:param string w: word to be added to T
:returns: new trie consisting of w added into T
:complexity: O(len(w))
"""
if T is None:
T = TrieNode()
if i == len(w):
T.is_word = True
else:
T.s[w[i]] = add(T.s[w[i]], w, i + 1)
return T
[docs]
def Trie(S): # Build the trie for the words in the dictionary S
"""
:param S: set of words
:returns: trie containing all words from S
:complexity: linear in total word sizes from S
"""
T = None
for w in S:
T = add(T, w)
return T
[docs]
def spell_check(T, w): # Spell check a word against the trie
"""Spellchecker
:param T: trie encoding the dictionary
:param w: given word
:returns: a closest word from the dictionary
:complexity: linear if distance was constant
"""
assert T is not None
dist = 0
while True:
u = search(T, dist, w)
if u is not None: # Match at distance dist
return u
dist += 1 # No match - try increasing the distance
# pylint: disable=too-many-return-statements, no-else-return
[docs]
def search(T, dist, w, i=0):
"""Searches for w[i:] in trie T with distance at most dist
"""
if i == len(w):
if T is not None and T.is_word and dist == 0:
return ""
else:
return None
if T is None:
return None
f = search(T.s[w[i]], dist, w, i + 1) # matching
if f is not None:
return w[i] + f
if dist == 0:
return None
for c in ascii_letters:
f = search(T.s[c], dist - 1, w, i) # insertion
if f is not None:
return c + f
f = search(T.s[c], dist - 1, w, i + 1) # substitution
if f is not None:
return c + f
return search(T, dist - 1, w, i + 1) # deletion
# snip}
```