DSA topic · Stage 7

Intervals interview preparation

Represent ranges and reason about overlap, ordering, and coverage.

DSA prep Practice 4 questions

Concept

Interval problems usually become manageable after sorting by a meaningful endpoint.

Complexity lens

Include sorting cost and define whether touching endpoints overlap.

Common mistakes

Using an unstated endpoint convention
Forgetting nested intervals
Comparing against the wrong merged boundary

Recognition

Decide from constraints, not labels.

These clues narrow the model. They do not replace an invariant or complexity check.

Recognition clues

Ranges overlap, cover, or compete for time
Ordering endpoints reveals merge or selection structure
The meaning of touching boundaries changes the answer

Implementation options

Sort and merge against the current accumulated interval
Sweep events with a stated tie rule
Heap for concurrent active intervals

Interview behavior

Clarify closed versus half-open endpoints
Explain the sort key and tie handling
Test nested, touching, and disjoint ranges

Patterns that operate on this topic

Merge IntervalsThe output prefix is fully merged and nonoverlapping; the current interval covers every processed input not already emitted.Two PointersEvery candidate outside the active pointer region has already been resolved or proved unable to improve the answer.

Representative problems

4 current Intervals questions.

Exact active distribution: 0 easy, 4 medium, 0 hard. External records contain metadata and original guidance only.

External catalogUnverified
Merge Intervals
Sort first, then compare each range with the active merged boundary.
Intervals Sorting Merge Intervals
MediumFree / publicSolve problem
External catalogUnverified
Sort Colors
Tests in-place partition reasoning beyond calling a sort function.
Sorting Intervals Arrays Two Pointers
MediumFree / publicSolve problem
External catalogUnverified
Minimum Number of Arrows to Burst Balloons
Provides a public interval-scheduling variation without requiring a premium Meeting Rooms problem.
Sorting Intervals Greedy Merge Intervals
MediumFree / publicSolve problem
External catalogUnverified
Insert Interval
Tests clean phase-based decomposition without resorting everything.
Sorting Intervals Merge Intervals
MediumFree / publicSolve problem

Review state

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Review prompts

Was the endpoint convention explicit?
Did I compare with the merged boundary or the prior input?
Would event ordering change a touch case?

Prerequisites and next step

Mix the patterns

Use an unlabeled set to test transfer after the topic-specific set.

Build a mixed set

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