array hash scan Pattern
Pattern hubs are for building transferable solving frames. Learn the recognition signals first, then drill state definition, update rules, and edge explanation until the pattern feels stable.
Pattern brief
Recognize first
Do you recognize how duplicate checks in rows, columns, and sub-boxes can be optimized using hash sets?
Solve rhythm
State the active state and invariant first, explain how each update preserves them, then pressure-test with counterexamples.
Most common miss
Confusing the 3x3 sub-box indexing, which can lead to missed duplicates or false positives.
Recognition signals
- Do you recognize how duplicate checks in rows, columns, and sub-boxes can be optimized using hash sets?
- Can you map each board cell to its 3x3 sub-box index without extra loops?
- Do you understand how backtracking helps with solving constraint satisfaction problems like Sudoku?
Solve flow
- 1. Define the active state/window.
- 2. Update state while preserving invariants.
- 3. Validate with edge-heavy examples.
Common misses
- Confusing the 3x3 sub-box indexing, which can lead to missed duplicates or false positives.
- Not properly updating hash sets after placing numbers, which could lead to incorrect checks for subsequent placements.
- Swapping incorrectly can lead to infinite loops or missed numbers.
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