hash table plus string 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
Check if the candidate correctly identifies the need for two hash maps to track character mappings.
Solve rhythm
State the active state and invariant first, explain how each update preserves them, then pressure-test with counterexamples.
Most common miss
Not checking for bijective mapping, which can cause mapping conflicts where multiple characters map to the same character.
Recognition signals
- Check if the candidate correctly identifies the need for two hash maps to track character mappings.
- Evaluate the candidate's ability to ensure bijective character mappings without conflicts.
- They may ask about handling large alphabets efficiently with hash maps.
Solve flow
- 1. Define the active state/window.
- 2. Update state while preserving invariants.
- 3. Validate with edge-heavy examples.
Common misses
- Not checking for bijective mapping, which can cause mapping conflicts where multiple characters map to the same character.
- Forgetting to mark the end-of-word flag, causing search to fail on full words.
- Using a hash table can lead to excessive space usage for large inputs.
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