#cycle detection

11 cycle detection interview questions, asked at Amazon, OpenAI, Airbnb and 9 more companies. Last asked Oct 2026.

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Mini spreadsheet with formulas and cycle detectionCodingBuild a mini spreadsheet with cell get and set, formula evaluation over dependencies, cached values with eager updates, and cycle detection. Covers the bank's spreadsheet variants…
Last asked Oct 2026
Follow one-way links to the endpoint or the last node before a loopCodingA network has nodes joined by one-way links, and each node links to at most one other node. Starting from a given node, follow the links and return the endpoint: the last node the…
Last asked Oct 2026
Course schedule: finish every course and find an orderCodingYou have n courses and a list of prerequisite pairs. 1. Decide whether every course can be completed. This fails exactly when the prerequisites contain a cycle. 2. Return one…
Last asked Jul 2026
Repair a looping bootloader programCodingA tiny bootloader stores its program as a list of text instructions. Each entry has the form "<op <value", where value is a signed integer. The machine has one accumulator, which…
Last asked Jul 2026
DAG utility with add, validate and queryCodingBuild a small directed-acyclic-graph helper: add edges, reject ones that would create a cycle, and answer reachability or ordering queries over the graph. Reported on…
Last asked Apr 2026
Detect and break cycles in pod dependenciesCodingYou have many pods, and a pod may depend on other pods. 1. Dependencies are directed. Report whether they contain a cycle, much like checking whether a course schedule can be…
Last asked Feb 2026
Build, validate and prune a computation graphCodingImplement a small graph of neural-network operations: add nodes and dependencies, check structural rules, detect cycles, and remove branches that do not contribute to the required…
Last asked Feb 2026
Intersection of two linked lists that may have cyclesCodingGiven the heads of two singly linked lists, each of which may or may not contain a cycle, decide whether they share a node and return the first shared node. Find where each list's…
Last asked Jan 2026
Course schedule: can every course be finished?CodingGiven a number of courses and prerequisite pairs, return whether it is possible to finish every course, which means the prerequisite graph has no cycle. Use Kahn's algorithm or…
Last asked Dec 2025
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Detect a cycle in a directed graphCodingDecide whether a directed graph contains a cycle, using depth-first search with node states or Kahn's topological sort. Variants that came up: start with a linked list (fast and…
Last asked Dec 2025
Happy numberCodingReplace a number with the sum of the squares of its digits and repeat. Return whether it reaches 1 or loops forever. Detect the loop with a set of seen values or with fast and…
Last asked Oct 2025