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import typing as t
from enum import Enum, auto
key = t.Sequence[t.Hashable]
class TrieResult(Enum):
FAILED = auto()
PREFIX = auto()
EXISTS = auto()
def new_trie(keywords: t.Iterable[key], trie: t.Optional[t.Dict] = None) -> t.Dict:
"""
Creates a new trie out of a collection of keywords.
The trie is represented as a sequence of nested dictionaries keyed by either single
character strings, or by 0, which is used to designate that a keyword is in the trie.
Example:
>>> new_trie(["bla", "foo", "blab"])
{'b': {'l': {'a': {0: True, 'b': {0: True}}}}, 'f': {'o': {'o': {0: True}}}}
Args:
keywords: the keywords to create the trie from.
trie: a trie to mutate instead of creating a new one
Returns:
The trie corresponding to `keywords`.
"""
trie = {} if trie is None else trie
for key in keywords:
current = trie
for char in key:
current = current.setdefault(char, {})
current[0] = True
return trie
def in_trie(trie: t.Dict, key: key) -> t.Tuple[TrieResult, t.Dict]:
"""
Checks whether a key is in a trie.
Examples:
>>> in_trie(new_trie(["cat"]), "bob")
(<TrieResult.FAILED: 1>, {'c': {'a': {'t': {0: True}}}})
>>> in_trie(new_trie(["cat"]), "ca")
(<TrieResult.PREFIX: 2>, {'t': {0: True}})
>>> in_trie(new_trie(["cat"]), "cat")
(<TrieResult.EXISTS: 3>, {0: True})
Args:
trie: The trie to be searched.
key: The target key.
Returns:
A pair `(value, subtrie)`, where `subtrie` is the sub-trie we get at the point
where the search stops, and `value` is a TrieResult value that can be one of:
- TrieResult.FAILED: the search was unsuccessful
- TrieResult.PREFIX: `value` is a prefix of a keyword in `trie`
- TrieResult.EXISTS: `key` exists in `trie`
"""
if not key:
return (TrieResult.FAILED, trie)
current = trie
for char in key:
if char not in current:
return (TrieResult.FAILED, current)
current = current[char]
if 0 in current:
return (TrieResult.EXISTS, current)
return (TrieResult.PREFIX, current)
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