Crossword

Fill the symmetric grid from numbered clues, across and down.

What it is

A square grid of white and black cells, conventionally with 180° rotational symmetry. Numbered white cells start the entries; each across and down entry has a clue. Every white cell belongs to both an across and a down word (fully checked grids), so each letter is confirmed twice.

How to play

Answer what you know, pencil what you suspect, and let crossings settle disagreements. Short entries recur across published puzzles (crosswordese rewards experience); long entries yield to patterns once a few crossings are in. In a well-made grid every letter is checked by two words, so a wrong guess collides quickly.

Purpose

The prestige word puzzle, and the hardest of the three word-grid crates: it needs a clued, scored wordlist, which is a data-acquisition problem as much as an algorithmic one. The crate exists because the grid-filling machinery is shared with wordfit; the wordlist quality is the ongoing investment.

History

Invented by Arthur Wynne — a Liverpudlian journalist — for the New York World, published 21 December 1913 as a diamond-shaped “Word-Cross”. The 1920s made it a craze; The Times of London capitulated in 1930; the cryptic tradition forked in Britain while American grids standardised on full checking and rotational symmetry.

This implementation

• Spec knobs: size, max_blocks, theme, difficulty.
• Generation: symmetric block placement under connectivity and minimum-word-length constraints, then backtracking fill with most-constrained-slot-first over the scored wordlist; clues come with the list entries.
• Guarantees: the grid is connected, symmetric, fully filled from the list, and every entry has a clue; the fill is deterministic per seed.
• Difficulty: wordlist scoring tier and grid openness (block count, average entry length), banded.