Word ladder length

BFS on implicit graph.

BFS graph strings

Implement `word_ladder(begin: str, end: str, word_list: list[str]) -> int`.

Each step must be a valid word in word_list. Return 0 if no path exists.

Constraints

All words same length; 1 ≤ len ≤ 10; word_list ≤ 5000.

Example

>>> word_ladder("hit","cog",["hot","dot","dog","lot","log","cog"])
5

45 points ~40 min

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Hints

BFS; for each word try changing every position to a-z; check against word_set.

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