hard

Word Ladder

Given a start word, an end word and a dictionary of equal-length words, find the length of the shortest transformation sequence from start to end where each step changes exactly one letter and every intermediate word is in the dictionary. Return 0 if impossible.

Constraints
  • 1 ≤ word length ≤ 10
  • 1 ≤ wordList.length ≤ 5000
  • Lowercase letters, all words distinct
Examples
in: begin = "hit", end = "cog", list = ["hot","dot","dog","lot","log","cog"]
out: 5
hit → hot → dot → dog → cog.

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