graph search 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 understand how BFS guarantees the shortest path in a word transformation sequence?
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 if `endWord` is in the `wordList` before starting the BFS, leading to unnecessary computation.
Recognition signals
- Do you understand how BFS guarantees the shortest path in a word transformation sequence?
- Can you explain why a hash table improves the performance of this problem?
- Do you understand how Depth-First Search can be applied to matrix traversal?
Solve flow
- 1. Define the active state/window.
- 2. Update state while preserving invariants.
- 3. Validate with edge-heavy examples.
Common misses
- Not checking if `endWord` is in the `wordList` before starting the BFS, leading to unnecessary computation.
- Failing to properly mark border 'O's as safe, leading to incorrect regions being transformed.
- Failing to mark visited cells, causing infinite loops or double-counting.
Recommended Ladder
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