Word Ladder

Change one letter per step, every rung a real word: WAIT to MIND in four moves.

What it is

Lewis Carroll’s “Doublets”, published in Vanity Fair in 1879 — he claimed to have invented it on Christmas Day 1877 for two bored young ladies. The form has been a puzzle-page staple ever since, and a computer-science standard (shortest paths in the one-letter-difference graph).

How to play

Fill each empty row with a word that differs from the row above by exactly one letter, arriving at the bottom word in the printed number of steps.

The implementation’s guarantees

• The shortest ladder is proven unique before publishing: a path-counting BFS over the vocabulary’s one-letter graph accepts an endpoint pair only when exactly one shortest path realises the printed length — so the answer key is the answer at that length, not one of several. Longer detours always exist; the claim is scoped to the rung count, and says so.
• A second, independent BFS in the tests re-verifies distance and path count for every published ladder, so the search and the claim cannot share a bug.
• ~590 common four-letter words ship built-in; custom lists work if all words share one length.
• Rating basis: rung_count (≤3 Easy, 4 Medium, more Hard).