backtracking pruning 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 handle empty input correctly to avoid unnecessary recursion?
Solve rhythm
State the active state and invariant first, explain how each update preserves them, then pressure-test with counterexamples.
Most common miss
Failing to prune paths when the current combination exceeds the input length, leading to unnecessary recursion.
Recognition signals
- Do you handle empty input correctly to avoid unnecessary recursion?
- Can you explain how pruning prevents generating invalid or partial combinations?
- Checks if you handle repeated use of candidates correctly.
Solve flow
- 1. Define the active state/window.
- 2. Update state while preserving invariants.
- 3. Validate with edge-heavy examples.
Common misses
- Failing to prune paths when the current combination exceeds the input length, leading to unnecessary recursion.
- Failing to prune when the path sum exceeds the target, causing unnecessary recursion.
- Not sorting candidates first, which complicates duplicate skipping.
Recommended Ladder
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