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06b0756b38 Improve crossword puzzle solver implementation (#14568 )

* Improve crossword puzzle solver implementation

The original `is_valid` returned `False` for any non-empty cell, which meant two words sharing a letter could never be placed together. Since crossword grids are built on exactly those intersections, this broke the core use case. Related to that, `remove_word` during backtracking blindly blanked every cell of the removed word, wiping out letters that belonged to already-placed crossing words. The fix snapshots the grid before placement and only clears cells that were empty beforehand. There was also a mutation bug: `words.remove(word)` does an O(n) scan and modifies state shared across the call stack, replaced here with a local slice per frame. On top of the fixes, the solver now tries the longest word first at each level, a standard "most-constrained variable" heuristic that cuts down backtracks significantly on larger inputs.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Refactor character check in crossword solver

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>

2026-09-17 16:31:42 +02:00

__init__.py

Add __init__.py files in all the directories (#2503 )

2020-09-28 19:42:36 +02:00

all_combinations.py

doctest all_combinations.py (#12506 )

2025-01-12 17:54:23 -08:00

all_permutations.py

docs: add docstring and doctests to generate_all_permutations) (#15055 )

2026-09-08 17:29:02 +02:00

all_subsequences.py

docs: add docstrings and doctests to generate_all_subsequences (#15090 )