Write a program that solves word-chain puzzles.

There’s a type of puzzle where the challenge is to build a chain of words, starting with one particular word and ending with another. Successive entries in the chain must all be real words, and each can differ from the previous word by just one letter. For example, you can get from “cat” to “dog” using the following chain.

1
2
3
4

  cat
  cot
  cog
  dog

The objective of this kata is to write a program that accepts start and end words and, using words from the dictionary, builds a word chain between them. For added programming fun, return the shortest word chain that solves each puzzle. For example, you can turn “lead” into “gold” in four steps (lead, load, goad, gold), and “ruby” into “code” in six steps (ruby, rubs, robs, rods, rode, code).

Once your code works, try timing it. Does it take less than a second for the above examples given a decent-sized word list? And is the timing the same forwards and backwards (so “lead” into “gold” takes the same time as “gold” into “lead”)?