Word Ladder

Word Ladder is the 1879 puzzle invented by Lewis Carroll (author of Alice in Wonderland) — he originally called it “Doublets.” Start with one word; change one letter at a time to form new valid words; end at a target word. Each intermediate word must be valid English. Word Ladder tests vocabulary, pattern matching, and lateral thinking.

How to play

• You’re given a starting word and target word, both of the same length.
• Change ONE letter to form a new valid word.
• Each step must produce a valid English word.
• Continue until you reach the target.
• Goal: minimize the number of steps.

Example

COLD → CORD → CORE → CARE → WARE → WARM. Cold to warm in 5 steps.

Beginner strategy

• Look at letter differences. If start and target differ in 4 letters, you need at least 4 changes.
• Each change must be valid. Don’t change a vowel to a consonant arbitrarily.
• Common word patterns. Common 4-letter words: CARE, BOOK, WORK, etc.
• Vowel chains. Change a vowel to another valid word; then change consonants.
• Reverse engineer. Start from the target and work backward.

Word Ladder math

• Search space. 4-letter words: ~3,000 valid English. 5-letter: ~10,000. Search graph is dense.
• BFS algorithm. Breadth-first search finds shortest paths in the word graph.
• NP-hard for arbitrary inputs. Worst case is computationally hard.

FAQ

• Q: Who invented Word Ladder? A: Lewis Carroll in 1879. Originally called “Doublets.”
• Q: Can I use any English word? A: Yes — common dictionary words only.
• Q: Minimum steps? A: At least the number of letter positions that differ between start and target.
• Q: Famous example? A: GREEN → GLEAM. Lots of intermediate words possible.

For other word games, try Anagram, Wordle, Word Scramble, or Word Search.