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Grokking the Coding Interview Patterns in Python

Solution: Word Ladder II

Explore how to solve the Word Ladder II problem by combining breadth-first search to identify shortest transformation sequences with depth-first search backtracking to reconstruct all valid paths. This lesson helps you understand efficient graph traversal and backtracking to handle complex word transformation challenges.

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Statement

You are given two words, beginWord and endWord, and a dictionary of words called wordList. Your task is to find all the shortest transformation sequences from beginWord to endWord, such that:

  1. Only one letter can be changed at a time.

  2. Each transformed word must exist in the given wordList.

  3. The transformation sequence must begin with beginWord and end with endWord.

Return all the shortest transformation sequences as a list of lists. If no valid transformation exists, return an empty list.

Constraints:

  • 1≤1 \leq beginWord.length ≤5\leq 5

  • endWord.length == beginWord.length

  • 1≤1 \leq wordList.length ≤500\leq 500 ...