#topological sort

30 topological sort interview questions, asked at Google, Amazon, Meta and 14 more companies. Last asked Oct 2026.

Work queue with a dead-letter queue and dependency cycle detectionCodingBuild an in-memory work queue for pipeline tasks that depend on each other (download, then tokenize, then train). Workers call nextready() to take a task and report back with…
Last asked Oct 2026
+4
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
Minimum time to finish dependent steps run in parallelCodingA job is split into n steps numbered 0 to n - 1; step i takes durationsi minutes. A pair u, v in dependencies means step u must finish before step v starts. Any number of steps…
Last asked Oct 2026
Find every recipe you can make from your suppliesCodingYou have an unlimited stock of some basic supplies and a book of recipes. Each recipe has a unique name and a list of ingredients; an ingredient can be a supply, the name of…
Last asked Oct 2026
+4
Group dependent tasks into parallel levelsCodingYou run a build system. Each task has a unique, non-empty lowercase name. Some tasks depend on others: a dependency before, after means before must finish before after can start…
Last asked Sep 2026
Effective privileges in a role hierarchy with allow and disallow listsCodingYou are building the access-control layer of a data platform. Every role has: - allowed: privileges granted directly to the role - disallowed: privileges explicitly taken away…
Last asked Sep 2026
Lexicographically smallest topological orderCodingGiven tasks and the dependencies between them, return an order that runs every task after the tasks it depends on. When several tasks are ready at once, always pick the smallest…
Last asked Sep 2026
Order dependent tasks and find what must rerunCodingGiven tasks and their prerequisites, return any valid order to run them, or detect that the dependencies form a cycle. Then, given a set of tasks that changed, find every task…
Last asked Sep 2026
+1
Alien dictionaryCodingYou get a list of words sorted in the dictionary order of an unknown alphabet. Derive an order of the letters that is consistent with it, or report that none exists. Explain how…
Last asked Aug 2026
Smallest valid task order from dependenciesCodingThere are n tasks numbered 0 to n - 1, done one at a time, and a list of pairs a, b meaning a must finish before b starts. Return an order that respects every dependency; among…
Last asked Aug 2026
Can two ordered sequences be merged into one order?CodingYou get two arrays of integer labels. Each array sets ordering rules: a label must come before every label that follows it in the same array. Decide whether one ordering exists…
Last asked Aug 2026
Dependency-safe deletion orderCodingEntities have parent-child relationships, and the relationships limit what can be deleted when. Model the relationships as a graph and return an order that deletes everything…
Last asked Aug 2026
Evaluate variable definitions with forward references and cyclesCodingA list of assignments defines variables with arithmetic expressions that may use variables defined later. Evaluate them all, then report which ones are undefined because they…
Last asked Aug 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
Alien dictionary with the smallest valid orderCodingYou get a list of words (password hints) that is sorted under an unknown alphabet. Work out an order of the characters that is consistent with that sorting, and when several…
Last asked Jun 2026
Deterministic task execution orderCodingGiven tasks and their dependencies, return an order to run them that respects every dependency and comes out the same every time for the same input, by a fixed rule for breaking…
Last asked Jun 2026
Alien dictionary: check sorted order, then infer the alphabetCoding1. You are given the order of letters in an unfamiliar alphabet and a list of words. Return whether the words are sorted according to that alphabet. 2. Now the alphabet is…
Last asked Jun 2026
Agent to-do list with task dependenciesCodingBuild the task tracker an AI agent uses to plan its work. The question comes in three parts. Each part builds on the one before, so keep earlier behavior working. A status is an…
Last asked May 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
Best-scoring ski run through a trail mapCodingA ski area has mapped its one-way trails between named checkpoints. The trail map has no cycles: once you ski down a trail you can never get back to where you were. Every trail…
Last asked Mar 2026
Build order for a package and its dependenciesCodinggetdependencies(package) returns a package's direct dependencies; the whole graph is not given up front. Given a target package, return an order in which to build it and…
Last asked Jan 2026
Order feature activations by their dependenciesCodingFeatures must be turned on in an order that respects their dependencies (a feature can only be activated after the features it depends on). Given the features and dependencies…
Last asked Jan 2026
Topological sort of a directed graphCodingReturn an order of a directed graph's nodes in which every edge goes from earlier to later, or report a cycle. Give Kahn's algorithm and the DFS version. Only the title of this…
Last asked Jan 2026
Minimum time to finish target courses in a prerequisite DAGCodingCourses form a directed acyclic graph of prerequisites and each course takes a given time; any number of courses can run at once as soon as their prerequisites are done. Return…
Last asked Dec 2025
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
Course schedule: detect a cycle and return an orderCodingCourses have prerequisites. Decide whether all courses can be finished (the prerequisite graph has no cycle), and if so return a valid order to take them. Use depth-first search…
Last asked Sep 2025
Validate a course catalog's prerequisitesCodingA course catalog lists each course and its prerequisites. Check that the catalog is valid: every prerequisite exists and there is no cycle, so all courses can be taken in some…
Last asked Aug 2025
Peel an N-ary tree one leaf layer per dayCodingEvery day, all leaves of an N-ary tree fall off at the same time. A leaf is a node with no children left. When a node loses its last child, it becomes a leaf and falls on the next…
Longest path in a DAG from an edge listCodingYou are given a directed acyclic graph as a list of edges. Each edge is a pair u, v of node names and means there is an edge from u to v. A node exists only if it appears in at…
+1
Find bottleneck dependencies in a parallel buildCodingYou are given n build targets numbered 0 to n - 1 and a list of directed edges edges. An edge u, v means target v cannot start building until target u has finished. The graph has…