Amazon SDE Interview Preparation Guide

Use breadth-first search with a FIFO queue, marking vertices when they are enqueued to avoid duplicate work. Track distance or parents according to the required output. On an adjacency-list representation the traversal is O(V + E); weighted edges require reconsidering the algorithm.

Check your understanding: Test a cycle, disconnected target, repeated edge and start equal to target.

Common trap: Applying unweighted BFS to arbitrary weighted shortest paths.

Concept reference: MIT OpenCourseWare: algorithm lecture notes

Identify a validity condition that can be restored by moving the left boundary as the right boundary advances. Maintain the information needed to check that condition, such as character frequencies. Explain why neither boundary moves backward and verify the invariant, rather than memorizing a template.

Check your understanding: Trace repeated characters and a window that shrinks several times in one step.

Common trap: Using a window when the validity condition is not monotone under shrinking.

Concept reference: MIT OpenCourseWare: algorithm lecture notes

State what information from earlier elements is needed and store exactly that information. Account for lookup assumptions, extra memory and duplicate handling. Compare against a simple reference implementation on small random inputs before measuring larger cases.

Check your understanding: Check duplicates, negative values and no-solution input against a brute-force oracle.

Common trap: Quoting O(n) without explaining the lookup or space assumptions.

Concept reference: MIT OpenCourseWare: algorithm lecture notes

First, identify technical constraints and define measurable service objectives. Next, trace the solution from requirement through implementation and verification. Contrast architectural trade-offs across simplicity, correctness, maintainability and scale, explicitly mitigate the risk of the same job is processed twice and produces conflicting side effects, and confirm system stability using lease-expiry tests, idempotency records and a restart recovery drill.

Common trap: Reaching for a specific library or framework before defining constraints, failure envelopes, and automated verification criteria.

Prioritise the failure mode exhibiting the highest user blast radius and lowest observability. Formulate an explicit containment boundary, implement idempotent retries with jitter, and establish an automated rollback threshold. Verify resilience through a server-authoritative timestamp trace and boundary property tests.

Common trap: Relying on passive monitoring dashboards without defining explicit error-budget alerts, rollback triggers, and verified recovery procedures.

Structure the response using Context-Decision-Tradeoff-Result: articulate the business and technical constraints, compare viable alternatives, explain the implementation (trace the solution from requirement through implementation and verification), and document the accepted trade-off. Provide concrete proof: a project example, measured result and repeatable verification step.

Common trap: Speaking only in high-level abstractions or team accomplishments without detailing your direct implementation decisions, trade-offs, and measured results.

Formulate a falsifiable hypothesis from observable telemetry before altering configurations. Then inspect the smallest failing example, boundary conditions, complexity and verification evidence. Isolate the defect to the smallest reproducible boundary, validate root cause with evidence, and confirm full resolution using semantic validation results, quarantine records and a replay verification.

Common trap: Applying speculative fixes or restarting services blindly without establishing an observable signal connected to a falsifiable hypothesis.

Produce a decision log with focused tests, complexity analysis and a measured result. Document baseline assumptions, technical mechanism (trace the solution from requirement through implementation and verification), rejected alternatives, bounded failure envelopes, and deterministic pass criteria. Supply reproducible verification via a compatibility test matrix and a staged rollout metric.

Common trap: Presenting architecture diagrams or slides lacking automated unit/integration tests, observable metrics, or automated rollback configurations.