Non-overlapping Intervals — Step-by-Step Visualization

Algorithm Pattern

Greedy (Sort by End Time)

Key Idea

Sort intervals by end time. Greedily keep each interval that doesn't overlap the previous kept one. Every overlap → one removal.

Step-by-Step Approach

1. Sort intervals by end time.
2. Track prevEnd = end of last kept interval.
3. For each interval: if start >= prevEnd, keep it (update prevEnd).
4. Otherwise it overlaps — remove it (res++).
5. Return res.

Common Gotchas

• Sort by END time, not start time.
• When two intervals overlap, always discard the one with the larger end (so we keep more future room) — sorting by end ensures this automatically.