mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-12-18 01:00:15 +00:00
43a47e01eb
* Add word ladder algorithm in backtracking * Improve comments and implement ruff checks * updating DIRECTORY.md * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Change BFS to Backtracking * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Incorporate PR Changes * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Add type hints for backtrack function * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci --------- Co-authored-by: Hardvan <Hardvan@users.noreply.github.com> Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
101 lines
3.6 KiB
Python
101 lines
3.6 KiB
Python
"""
|
|
Word Ladder is a classic problem in computer science.
|
|
The problem is to transform a start word into an end word
|
|
by changing one letter at a time.
|
|
Each intermediate word must be a valid word from a given list of words.
|
|
The goal is to find a transformation sequence
|
|
from the start word to the end word.
|
|
|
|
Wikipedia: https://en.wikipedia.org/wiki/Word_ladder
|
|
"""
|
|
|
|
import string
|
|
|
|
|
|
def backtrack(
|
|
current_word: str, path: list[str], end_word: str, word_set: set[str]
|
|
) -> list[str]:
|
|
"""
|
|
Helper function to perform backtracking to find the transformation
|
|
from the current_word to the end_word.
|
|
|
|
Parameters:
|
|
current_word (str): The current word in the transformation sequence.
|
|
path (list[str]): The list of transformations from begin_word to current_word.
|
|
end_word (str): The target word for transformation.
|
|
word_set (set[str]): The set of valid words for transformation.
|
|
|
|
Returns:
|
|
list[str]: The list of transformations from begin_word to end_word.
|
|
Returns an empty list if there is no valid
|
|
transformation from current_word to end_word.
|
|
|
|
Example:
|
|
>>> backtrack("hit", ["hit"], "cog", {"hot", "dot", "dog", "lot", "log", "cog"})
|
|
['hit', 'hot', 'dot', 'lot', 'log', 'cog']
|
|
|
|
>>> backtrack("hit", ["hit"], "cog", {"hot", "dot", "dog", "lot", "log"})
|
|
[]
|
|
|
|
>>> backtrack("lead", ["lead"], "gold", {"load", "goad", "gold", "lead", "lord"})
|
|
['lead', 'lead', 'load', 'goad', 'gold']
|
|
|
|
>>> backtrack("game", ["game"], "code", {"came", "cage", "code", "cade", "gave"})
|
|
['game', 'came', 'cade', 'code']
|
|
"""
|
|
|
|
# Base case: If the current word is the end word, return the path
|
|
if current_word == end_word:
|
|
return path
|
|
|
|
# Try all possible single-letter transformations
|
|
for i in range(len(current_word)):
|
|
for c in string.ascii_lowercase: # Try changing each letter
|
|
transformed_word = current_word[:i] + c + current_word[i + 1 :]
|
|
if transformed_word in word_set:
|
|
word_set.remove(transformed_word)
|
|
# Recur with the new word added to the path
|
|
result = backtrack(
|
|
transformed_word, [*path, transformed_word], end_word, word_set
|
|
)
|
|
if result: # valid transformation found
|
|
return result
|
|
word_set.add(transformed_word) # backtrack
|
|
|
|
return [] # No valid transformation found
|
|
|
|
|
|
def word_ladder(begin_word: str, end_word: str, word_set: set[str]) -> list[str]:
|
|
"""
|
|
Solve the Word Ladder problem using Backtracking and return
|
|
the list of transformations from begin_word to end_word.
|
|
|
|
Parameters:
|
|
begin_word (str): The word from which the transformation starts.
|
|
end_word (str): The target word for transformation.
|
|
word_list (list[str]): The list of valid words for transformation.
|
|
|
|
Returns:
|
|
list[str]: The list of transformations from begin_word to end_word.
|
|
Returns an empty list if there is no valid transformation.
|
|
|
|
Example:
|
|
>>> word_ladder("hit", "cog", ["hot", "dot", "dog", "lot", "log", "cog"])
|
|
['hit', 'hot', 'dot', 'lot', 'log', 'cog']
|
|
|
|
>>> word_ladder("hit", "cog", ["hot", "dot", "dog", "lot", "log"])
|
|
[]
|
|
|
|
>>> word_ladder("lead", "gold", ["load", "goad", "gold", "lead", "lord"])
|
|
['lead', 'lead', 'load', 'goad', 'gold']
|
|
|
|
>>> word_ladder("game", "code", ["came", "cage", "code", "cade", "gave"])
|
|
['game', 'came', 'cade', 'code']
|
|
"""
|
|
|
|
if end_word not in word_set: # no valid transformation possible
|
|
return []
|
|
|
|
# Perform backtracking starting from the begin_word
|
|
return backtrack(begin_word, [begin_word], end_word, word_set)
|