How should I practice Mutable Table Aggregations?

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Mutable Table Aggregations

Notion● MediumFULLTIMEPHONE SCREENONSITE INTERVIEW

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Problem statement

Maintain integer-valued rows across independent tables. Process these operations:

["ADD", tableId, rowId, value] inserts a new row.
["UPDATE", tableId, rowId, value] replaces an existing row's value.
["DELETE", tableId, rowId] removes an existing row.
["QUERY", tableId] returns count|sum|average|max for that table.

Format a non-empty table's average with exactly two digits after the decimal point. For an empty table, return 0|0|0.00|NULL. Return the values produced by QUERY operations in order.

Function

runTableAggregations(operations: String[][]) → String[]

Examples

Example 1

operations = [["ADD","docs","r1","10"],["ADD","docs","r2","20"],["QUERY","docs"],["UPDATE","docs","r1","40"],["QUERY","docs"],["DELETE","docs","r2"],["QUERY","docs"]]return = ["2|30|15.00|20","2|60|30.00|40","1|40|40.00|40"]

The first query aggregates two rows. Updating r1 changes sum, average, and maximum; deleting r2 leaves one row.

Constraints

1 <= operations.length <= 20000.
Table and row IDs are non-empty ASCII strings containing neither | nor whitespace.
Values are decimal integers in [-10^9, 10^9].
An ADD row ID is absent from that table; an UPDATE or DELETE row ID is present.
Every table contains at most 10000 rows, and every sum fits a signed 64-bit integer.