iframe-proxy | Sunbelt Computer Software

History

100 lines (77 loc) · 3.64 KB

Raw

100

"""

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)

Sunbelt Computer Software

PL/B Language Development and Support

Navigation Menu

Sunbelt Computer Software

PL/B Language Development and Support

FilesExpand file tree

word_ladder.py

Latest commit

History

word_ladder.py

File metadata and controls