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ITA, Skyscanner

SystemTechniques · 5Primitives · 24 flight-search K shortest pathsgraphs · medium: Yen's / Eppstein's k shortest loopless paths for alternative itinerariesRaptor transit routinggraphs · medium: Round-based public transit / schedule routing (RAPTOR) with Pareto setsGradient-boosted decision trees (GB…machine-learning · medium: Add small regression trees one at a time, each fitted to the loss gradient; histogram splits over 256 bins make it the strongest tabular default.›Learning to rankmachine-learning · medium: Train a scorer on query-grouped data so that the order it induces maximizes NDCG; LambdaMART (boosted trees with NDCG-weighted pair gradients) is the production default.›Rete rules enginesystems · medium: Match many rules against changing facts by caching partial matches in a shared network, so each change only does the work it actually affects.›Calendar date arithmeticsystems · low: Civil dates, time zones (tzdb), DST gaps, month-end anchoring and duration mathConsistent hashingdistributed · low: Hash nodes and keys onto a ring; each key belongs to the next node clockwise, so membership changes move only about 1/n of keys.›Currency cross rate triangulationfinance · low: Deriving cross rates through a base currency with correct precision, inversion and spreadsMoney representationfinance · low: Store money as integer minor units with an explicit currency exponent, compute in wider integers, and round once with a named rounding mode.›Top-k selectionsearch-sort · low: Keep the k best of n items without sorting all n - bounded min-heap for streams, quickselect for arrays, threshold pruning to skip most items.›Circuit breakersystems · low: Stop calling a failing dependency for a while, probe it with trial calls, and resume on recovery: fail fast instead of piling up timeouts.›Hedged requestssystems · low: Sending a backup request after a latency percentile and taking the first answer to cut tail latencyStale while revalidatesystems · low: Serving cached data past TTL while refreshing in the background, with request coalescingToken bucketsystems · low: A bucket of up to b tokens refilled at rate r; requests spend tokens, enforcing an average rate while allowing bursts of b.›W-TinyLFUsystems · low: An LRU window plus segmented LRU, guarded by a 4-bit Count-Min sketch that admits a newcomer only if it beats the victim's frequency.›d-ary heapdata-structures · low: Array heap with d children per node (d = 4 typical): half the binary heap's depth, siblings in one cache line, faster priority queues.›Dijkstra's algorithmgraphs · low: Single-source shortest paths with non-negative edge weights by settling vertices in order of distance with a priority queue.›BFS and DFSgraphs · low: The two basic graph traversals; BFS gives hop distances and levels, DFS gives discovery/finish order for cycles, components and topological order.›Quantile sketchesdata-structures · low: Mergeable quantile sketches: t-digest, DDSketch, HDR histogramsLoss functionsmachine-learning · low: The scalar a model minimizes: cross-entropy for classes and tokens, MSE or Huber for values, each with a stable form and simple gradient.›Regularizationmachine-learning · low: Techniques that trade training fit for generalization: weight decay, dropout, early stopping, label smoothing and data mixing, with the exact update rules and defaults.›+ 8 more primitives

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