You sort the [start, end] pairs by start and scan once. That single pass answers overlap and merge questions without comparing every pair.

Earn the full sheet below.

When to use it

• You get [start, end] pairs and need to find or merge overlaps.
• The problem talks about meetings, schedules, or conflicting ranges.
• Sorting by start turns pairwise comparison into a single scan.
• If you need the one right of a target, use Modified Binary Search.

What's on the sheet

The whole trick is to sort, scan, and merge. Step 3 decides what overlap means.

1. Sort by start. Sorting turns overlap checks into one left-to-right scan.
2. Unpack the pair. a is the interval you kept; b is the one you just met.
3. Check for overlap. Decide what happens when two intervals touch.
4. Return. Hand back whatever the scan built.

Watch out

• Sort by start, not by end. The overlap check (b_start <= a_end) assumes starts are in order.
• Use <= rather than <. Back-to-back intervals like [1, 3] and [3, 5] usually count as overlapping.
• Meeting Rooms I just needs a yes or no on the first overlap. Skip the merged list.

How to earn it

Solve half of the Intervals problems and the sheet is yours. A free account works fine, and everyone earns their sheets the same way.

Want to see a finished sheet first? Preview the Two Pointers sample.

Every pattern has a sheet. See the full set.