Track Package Receipt Gaps
Amazon● MediumFULLTIMEPHONE SCREENProblem statement
Process a finite sequence of package-receipt operations. Each row of operations has one of these forms:
["receive", packageId]records the nonnegative package ID written as a decimal string. Receiving the same ID again has no additional effect.["report"]produces one snapshot of the received IDs.
For a report, let maxReceived be the largest received ID, or -1 when no package has been received. Let prefixEnd be the largest value such that every ID from 0 through prefixEnd has been received. If ID 0 has not been received, prefixEnd is -1.
Encode each report as [prefixEnd, maxReceived, missingId1, missingId2, ...], where the missing IDs are every absent value from 0 through maxReceived in increasing order. Thus, an empty state produces [-1, -1]. Return the report rows in operation order.
Function
packageReceiptReports(operations: String[][]) → int[][]Examples
Example 1
operations = [["receive","2"],["receive","0"],["report"],["receive","1"],["report"]]return = [[0,2,1],[2,2]]At the first report, IDs 0 and 2 have arrived. The contiguous prefix ends at 0, the maximum is 2, and ID 1 is missing. After receiving ID 1, the complete prefix ends at 2 and there are no gaps.
Example 2
operations = [["report"],["receive","3"],["receive","3"],["report"],["receive","0"],["report"]]return = [[-1,-1],[-1,3,0,1,2],[0,3,1,2]]The first report observes no packages. Receiving ID 3 twice records it once. After ID 0 arrives, the contiguous prefix advances to 0, while IDs 1 and 2 remain missing.
Constraints
1 <= operations.length <= 100000.- Every operation is either
["receive", packageId]or["report"]. - Every package ID is a canonical decimal string for an integer in
[0, 200000]. - The total number of integers across all returned report rows is at most
200000. - Operations are applied strictly from left to right.