Implement Router
A medium-tier problem at 22% community acceptance, tagged with Array, Hash Table, Binary Search. Reported in interviews at Cisco and 0 others.
Implement Router is a low-acceptance design problem that asks you to build a routing system from scratch. Cisco has asked it, and at 21% acceptance, most candidates either miss the data structure choice or fail under the performance constraints. You'll need to pick the right combination of Hash Table, Array, and Binary Search to handle route matching efficiently. If you blank on the ordering strategy or priority logic during your assessment, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Implement Router"
Implement Router is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an Amazon engineer who used it to pass JPMorgan's OA and system design loop.
Get StealthCoderThe trap here is conflating simple hash lookup with route matching. Routes often have wildcard patterns or prefix hierarchies that demand ordered comparison, not just O(1) direct access. Most candidates build a naive Hash Table solution, then hit timeouts or wrong answers when the problem requires you to match against multiple route patterns with specificity rules. Binary Search shines when you sort routes by priority, and the problem usually hinges on understanding that you can't just store and retrieve. You'll likely need Array ordering plus Hash Table for fast component lookup, sometimes with a Queue for breadth-first traversal depending on the routing graph structure. The design component isn't about creativity; it's about recognizing which structure solves the bottleneck. If this problem hits your live OA and you freeze on the matching logic, StealthCoder runs invisible during screen share and delivers a working implementation.
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Implement Router recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an Amazon engineer who used it to pass JPMorgan's OA and system design loop. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Implement Router interview FAQ
How do I know if Hash Table alone will pass this problem?+
Hash Table alone fails when the problem requires pattern matching or priority-based route selection rather than exact key lookup. If routes have wildcards, prefixes, or specificity rules, you need ordering. Check whether the input examples include partial matches or multiple valid routes; that's your signal to add Binary Search or Ordered Set for precedence.
What's the most common failure mode at 21% acceptance?+
Candidates build a flat Hash Table, then realize they can't efficiently find the best matching route when multiple patterns apply. The second failure is ignoring that route ordering matters. You'll likely need to sort by specificity (longest prefix, or explicit priority) and use Binary Search to find the match, not just iterate and check.
When would I use Queue in a router design?+
Queue appears when the problem involves breadth-first traversal of a routing tree or graph, or when you need to process routes in FIFO order during initialization or updates. If the routing system is a flat lookup without graph structure, Queue won't help. Check whether routes form a tree or network.
Is Cisco still asking this in 2024?+
This problem has low frequency overall, but Cisco has reportedly asked it. Design problems like this tend to resurface in infrastructure or networking-focused roles. It's not a mainstream LeetCode grind, so drilling it is lower ROI than system design rounds, but if you're interviewing at networking companies, it's worth recognizing.
How do I test whether my route matching logic is correct?+
Build a few test cases: exact match, no match, multiple valid matches with different specificities, and edge cases like empty routes or default routes. The problem likely penalizes wrong priority, not just missed matches. Run each test by hand and verify your ordering logic returns the highest-priority match first.
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