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Word Ladders - Medium


Word ladder is a word game invented by Lewis Carroll. A word ladder puzzle begins with two words, and to solve the puzzle one must find a chain of other words to link the two, in which two adjacent words (that is, words in successive steps) differ by one letter. Eg. SPORT <-> SHORT
Source: Wikipedia

If you've followed my previous Dijkstra's Shortest Path Algorithm Tutorial, you'll be able to solve this challenge with minimum effort.

Essentially, we create a graph where each word is a vertex and there exists an edge if two words differ by a single character. To find the word ladder is basically running any shortest path algorithm. You could also use a Breadth First Search.

Some important observations

  • The length of the source and destination words must be the same for a path to exist.
  • The path from source to destination  can only contain words of the same length. So we can prune off the rest of the dictionary.
  • The graph is undirected.
Here's my implementation, it uses the modules from the tutorial.



To run the program, "wordladder.py SOURCE DESTINATION < dict.txt"
For eg.

C:\>wordladder.py BOX TEN < words.txt
(4, ['BOX', 'BOD', 'BED', 'BEN', 'TEN'])
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