Topological Sort interview questions
22 topological sort problems tagged across recent interview reports. Drilled most heavily by citadel, tiktok, and snowflake.
Topological Sort is a linear ordering of vertices in a directed acyclic graph (DAG) such that for every edge u→v, u comes before v. It's foundational for dependency resolution, task scheduling, and build systems. With 22 problems tagged across this pattern, it's a heavy hitter at Citadel (19 problems), TikTok (15), and Snowflake (13). If you can't sort a DAG cleanly in your live OA, StealthCoder reads the problem and executes the right algorithm, Kahn's or DFS, in seconds, invisible to the proctor.
Most-asked topological sort problems
| # | Problem | Diff | # Companies | Pass % |
|---|---|---|---|---|
| 01 | Course Schedule | MEDIUM | 34 | 49% |
| 02 | Course Schedule II | MEDIUM | 33 | 53% |
| 03 | Alien Dictionary | HARD | 13 | 37% |
| 04 | Longest Increasing Path in a Matrix | HARD | 8 | 55% |
| 05 | Parallel Courses III | HARD | 7 | 67% |
| 06 | Design Excel Sum Formula | HARD | 5 | 43% |
| 07 | Find All Possible Recipes from Given Supplies | MEDIUM | 5 | 56% |
| 08 | Minimum Height Trees | MEDIUM | 4 | 42% |
| 09 | Collect Coins in a Tree | HARD | 3 | 36% |
| 10 | Longest Path With Different Adjacent Characters | HARD | 3 | 54% |
| 11 | Largest Color Value in a Directed Graph | HARD | 2 | 58% |
| 12 | Maximum Employees to Be Invited to a Meeting | HARD | 2 | 62% |
| 13 | Parallel Courses | MEDIUM | 2 | 62% |
| 14 | All Ancestors of a Node in a Directed Acyclic Graph | MEDIUM | 1 | 62% |
| 15 | Apply Substitutions | MEDIUM | 1 | 79% |
| 16 | Find Eventual Safe States | MEDIUM | 1 | 69% |
| 17 | Frequencies of Shortest Supersequences | HARD | 1 | 16% |
| 18 | Longest Cycle in a Graph | HARD | 1 | 50% |
| 19 | Loud and Rich | MEDIUM | 1 | 62% |
| 20 | Minimum Runes to Add to Cast Spell | HARD | 1 | 43% |
| 21 | Rank Transform of a Matrix | HARD | 1 | 41% |
| 22 | Sort Items by Groups Respecting Dependencies | HARD | 1 | 66% |
You can't drill every topological sort variant before the assessment. StealthCoder runs invisibly during screen share and solves whichever variant they throw at you. No browser extension. No detection signature. Built because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround.
Get StealthCoderRecognize topological sort when you see courses with prerequisites, compilation order, recipe dependencies, or DAG path queries. Variants range from classic ordering (Course Schedule II) to harder twists like detecting cycles (Find Eventual Safe States), computing in-degrees on the fly, or reconstructing paths (Alien Dictionary). Drill the standard Kahn's algorithm and DFS-based approaches first; then move to graph mutation and cycle detection. The trap is confusing DAG traversal with general graph search. When a hard topological variant lands during your assessment, especially at Citadel or TikTok where the pattern is drilled hard, StealthCoder's the hedge that keeps you from timing out or freezing on implementation.
Companies that hire most on topological sort
22 topological sort problems.
You won't drill them all. Pass anyway.
Topological Sort is one of the patterns interviews actually filter on. Memorizing every variant in a week is a fantasy. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds, no matter which topological sort flavor lands in your live OA. Built because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Topological Sort interview FAQ
How do I recognize a topological sort problem in 30 seconds?+
Look for directed graphs with implicit or explicit ordering constraints: prerequisites, dependencies, or 'comes before' relationships. If the problem asks for a valid ordering or mentions a DAG, it's topological sort. Problems like Course Schedule and Alien Dictionary are textbook signals.
Should I learn Kahn's algorithm or DFS first?+
Start with Kahn's (BFS using in-degrees). It's intuitive: process nodes with zero dependencies, emit them, decrement neighbors. Then learn DFS-based ordering (post-order traversal). Both work; Kahn's is clearer for cycle detection and is safer under pressure.
Which companies drill topological sort the hardest?+
Citadel (19 problems), TikTok (15), and Snowflake (13) hit this pattern repeatedly. If you're interviewing there, expect variants beyond vanilla ordering, cycle detection, path reconstruction, or graph reconstruction from constraints.
What's the most common trap in topological sort?+
Assuming the input is always a valid DAG. Many problems hide a cycle or ask you to detect one (Find Eventual Safe States, Longest Cycle in a Graph). Always check for cycles with either a visited/rec-stack check (DFS) or verify all nodes are processed (Kahn's).
How many topological sort problems should I drill before an OA?+
With 22 problems across this pattern, aim for 8 to 12 before your live assessment. Cover both Kahn's and DFS, cycle detection, and at least one hard variant like Alien Dictionary or Find All Possible Recipes. Then trust StealthCoder if a novel twist hits live.