Word ladder solver

Give it two five-letter words and it finds the shortest ladder between them, changing one letter at a time with every rung a real word.

This is the same breadth-first search that sets par on the daily Break 5 puzzle, running over the same 8,000-word dictionary. Use it to settle an argument, to check a pair you invented, or to see how a route you missed was supposed to go.

One rule: while today's puzzle is live, the solver will not touch either of its two words. The leaderboard is only worth topping if everyone climbed the ladder themselves. Both words are available again at midnight.

How the solver works

Every five-letter word in the dictionary is a point, and two points are joined when the words differ by exactly one letter. STONE joins STORE, STOLE, ATONE and about a dozen others. Finding a ladder is then just finding a path through that network, and finding the shortest ladder is a breadth-first search: check everything one move away, then everything two moves away, and so on until the target turns up. The first route that reaches it is guaranteed to be the shortest, and on a graph this size it takes a few milliseconds.

The interesting part is which words you allow. Break 5 keeps two answers:

• Par is the shortest route through everyday words only, so it is always solvable with vocabulary you already have. This is the number the daily puzzle sets you.
• Shortest is the shortest route through the whole dictionary, obscure words included. It sometimes beats par by a move or two, and we only show it when it does.

Some pairs have no ladder at all. A word whose neighbours are all dead ends sits in its own little island, and no amount of searching connects it to the mainland. The solver will tell you when that is what has happened rather than leaving you guessing.

Want to play rather than solve? Today's word ladder is free and takes about five minutes, or read what a word ladder is for the history and the strategy.