Load Balancing And Resource Lifecycle Simulation

What's being tested

These problems test stateful simulation with deterministic load-balancing behavior: routing, locking, lifecycle transitions, eviction, and shutdown handling. Interviewers are probing whether you can turn ambiguous product rules into clean data structures, preserve invariants, and handle edge cases without overcomplicating the code.

Patterns & templates

• Entity state maps — use dict[id] -> state for connections, accounts, or targets; most operations should be O(1) average time.

• Round-robin pointer — maintain next_index; after choosing a target, advance modulo n, skipping unavailable or full targets carefully.

• Capacity-aware routing — track load[target] and reject or reroute when load[target] == capacity[target]; define deterministic tie-breaking upfront.

• Sticky assignment — keep connection_id -> target; duplicate connect should usually return existing assignment, not consume capacity again.

• Lifecycle transitions — model connect, disconnect, shutdown, lock, unlock, and evict as explicit state changes with invariant checks.

• LRU cache template — combine dict plus doubly linked list or OrderedDict; get/put/evict are O(1).

• Ordered rerouting on shutdown — collect affected connections in stable order, free old capacity, then reassign deterministically to avoid hidden ordering bugs.

Common pitfalls

Pitfall: Treating duplicate connects as new connections, which silently inflates load and breaks capacity invariants.

Pitfall: Updating the round-robin pointer on failed assignment; clarify whether failed attempts should advance before coding.

Pitfall: Handling shutdown by deleting a server first, then losing the list or order of connections that must be rerouted.

Practice these

The practice cards below cover the canonical variants — solve all of them and time yourself.