array plus segment tree 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 candidates handle very large X coordinates efficiently.
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 compress coordinates, causing memory overflow for large lefti values.
Recognition signals
- Check if candidates handle very large X coordinates efficiently.
- Look for proper use of range maximum queries using a segment tree or ordered set.
- Candidate demonstrates understanding of the Line Sweep technique.
Solve flow
- 1. Define the active state/window.
- 2. Update state while preserving invariants.
- 3. Validate with edge-heavy examples.
Common misses
- Failing to compress coordinates, causing memory overflow for large lefti values.
- Misunderstanding the use of the Segment Tree and treating each rectangle independently.
- Updating nums1 naively for every flip causes TLE on large inputs.
Recommended Ladder
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