Improve crossword puzzle solver implementation#14568
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Ewanjohndennis wants to merge 3 commits intoTheAlgorithms:masterfrom
Open
Improve crossword puzzle solver implementation#14568Ewanjohndennis wants to merge 3 commits intoTheAlgorithms:masterfrom
Ewanjohndennis wants to merge 3 commits intoTheAlgorithms:masterfrom
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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.
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The original
is_validreturnedFalsefor 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_wordduring 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.Describe your change:
Checklist: