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A three-order moving averageHardSQLSQLHard15 minFirst and latest order per customer, on every rowHardSQLSQLHard13 minFiltering on a rankingHardSQLSQLHard14 minRuns of consecutive active daysHardSQLMeta styleSQLMeta styleHard18 minCumulative distinct users by dayHardSQLSQLHard15 minThe latest subscription per account, without a windowHardSQLSQLHard14 minHow long each cancelled subscription lastedHardSQLSQLHard15 minAverage value per unit, without dividing by zeroHardSQLSQLHard13 minEvery warehouse crossed with every itemHardSQLSQLHard15 minCourses nobody has been graded onHardSQLSQLHard14 minPairs of students sharing a courseHardSQLSQLHard15 minMoney in and money out, per accountHardSQLSQLHard14 min
ROC-AUC computationHardWrite codeMeta styleWrite codeMeta styleHard30 minTF-IDF scoringHardWrite codeMeta styleWrite codeMeta styleHard30 minDecision stump Gini splitHardWrite codeMeta styleWrite codeMeta styleHard35 minCollaborative filtering predictionHardWrite codeNetflix styleWrite codeNetflix styleHard35 minPivot sparse recordsHardWrite codeDatabricks styleWrite codeDatabricks styleHard35 minParse nested listHardWrite codeStripe styleWrite codeStripe styleHard35 minParse CSV lineHardWrite codeStripe styleWrite codeStripe styleHard35 minDigit sum 0 to nHardWrite codeWrite codeHard35 minBST k-th smallestHardWrite codeMeta styleWrite codeMeta styleHard35 minBasic calculatorHardWrite codeMeta styleWrite codeMeta styleHard30 minTop k items per categoryHardWrite codeDatabricks styleWrite codeDatabricks styleHard35 minJSON subset parserHardWrite codeStripe styleWrite codeStripe styleHard40 minOrder-statistics multisetHardWrite codeCitadel styleWrite codeCitadel styleHard40 minExpression evaluatorHardWrite codeMeta styleWrite codeMeta styleHard35 minDecode ways with wildcardsHardWrite codeAmazon styleWrite codeAmazon styleHard32 minJSON parserHardWrite codeStripe styleWrite codeStripe styleHard40 minSessionize clickstreamHardWrite codeDatabricks styleWrite codeDatabricks styleHard35 minKth smallest dynamic setHardWrite codeWrite codeHard35 minChemical formula parserHardWrite codeWrite codeHard35 minLinear regression gradient stepHardWrite codeOpenAI styleWrite codeOpenAI styleHard30 minJWT token parsingHardWrite codeStripe styleWrite codeStripe styleHard28 minSafe columns to dropHardWrite codeDatabricks styleWrite codeDatabricks styleHard35 minDays of service at a cut-off dateHardData framesData framesHard12 minDistance from the team averageHardData framesData framesHard12 minMost recent order for each customerHardData framesData framesHard13 minPaid and total orders per customerHardData framesData framesHard12 minAverage score per student per subject, with gaps filledHardData framesData framesHard12 min
Fewest moves to reorder keyed childrenHardWrite codeWrite codeHard35 minResolve flexible widths in a flex rowHardWrite codeWrite codeHard45 minAccessible names from a simplified treeHardWrite codeWrite codeHard45 minEvent loop output orderHardWrite codeWrite codeHard40 minFewest forced layouts for a batch of DOM reads and writesHardWrite codeWrite codeHard40 min
Internet checksumHardWrite codeCisco styleWrite codeCisco styleHard25 minCapability token verificationHardWrite codeStripe styleWrite codeStripe styleHard30 minSession token fixation detectionHardWrite codeStripe styleWrite codeStripe styleHard30 minSanitize HTML with a tag allowlistHardWrite codeWrite codeHard45 minVerify an append-only log with a consistency proofHardWrite codeWrite codeHard45 min