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Longest subarray GCDHardWrite codeWrite codeHard35 minChinese remainder theoremHardWrite codeCitadel styleWrite codeCitadel styleHard35 minPrimes in rangeHardWrite codeCitadel styleWrite codeCitadel styleHard30 minExtended Euclidean algorithmHardWrite codeWrite codeHard30 minCatalan number modulo primeHardWrite codeCitadel styleWrite codeCitadel styleHard30 minMiller-Rabin primality testHardWrite codeCitadel styleWrite codeCitadel styleHard35 minGeometric series moduloHardWrite codeWrite codeHard30 minFibonacci moduloHardWrite codeWrite codeHard35 minCoprime pairs mobius inversionHardWrite codeWrite codeHard35 minDiscrete logarithm modulo primeHardWrite codeWrite codeHard40 minSolve two congruencesHardWrite codeWrite codeHard35 min
Every employee with their departmentEasySQLSQLEasy8 minHeadcount per departmentEasySQLSQLEasy8 minOrders per statusEasySQLSQLEasy7 minThe highest and lowest salary on recordEasySQLSQLEasy7 minWho has no salary recordedEasySQLSQLEasy8 minOrders with the customer countryEasySQLSQLEasy8 minHow many of each eventEasySQLSQLEasy7 minMonthly revenue from live subscriptionsEasySQLSQLEasy8 minPosts with their authorEasySQLSQLEasy8 minAuthors with no country on fileEasySQLSQLEasy8 minHow many students per courseEasySQLSQLEasy8 minDepartments with nobody in themMediumSQLSQLMedium10 minThe average that a NULL salary ruinsMediumSQLSQLMedium10 minCustomers who spent over a thresholdMediumSQLSQLMedium10 minEveryone and their managerMediumSQLSQLMedium12 minSalaries paid to more than one personMediumSQLSQLMedium10 minPaid more than their department averageMediumSQLSQLMedium12 minRevenue by monthMediumSQLSQLMedium10 minA salary column with no blanksMediumSQLSQLMedium9 minHires per yearMediumSQLSQLMedium10 minManagers onlyMediumSQLSQLMedium10 minPayroll by department, biggest firstMediumSQLSQLMedium10 minCustomers who never orderedMediumSQLSQLMedium10 minAverage order value by countryMediumSQLSQLMedium10 minCountries that buy but never refundMediumSQLSQLMedium11 minSigned up and never came backMediumSQLSQLMedium10 minEvents by planMediumSQLSQLMedium10 minChurned accounts and whenMediumSQLSQLMedium10 minAccounts that subscribed more than onceMediumSQLSQLMedium11 minLive and churned MRR per tierMediumSQLSQLMedium11 minComment count per postMediumSQLSQLMedium10 minAuthors who have never commentedMediumSQLSQLMedium10 minPeople who commented on the same post twiceMediumSQLSQLMedium11 minThe balance of every accountMediumSQLSQLMedium10 minCash movement by monthMediumSQLSQLMedium11 minBoth sides of every transactionMediumSQLSQLMedium11 minWhat each warehouse holdsMediumSQLSQLMedium11 minThe value of each warehouseMediumSQLSQLMedium10 minAverage grade, ungraded excludedMediumSQLSQLMedium12 min