How should I practice Net Position Calculation from API Snapshots?

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Net Position Calculation from API Snapshots

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Problem statement

Calculate the final signed share quantity for each symbol from two supplied response tables. For this exercise, assume these arrays are immutable materialized responses from two read-only APIs; no live API calls or networking are required.

initialPositions contains rows [symbol, signedDecimalQuantity]. Initial symbols are unique. A symbol absent from this table starts at zero.
fills contains rows [symbol, side, positiveDecimalQuantity], with side exactly BUY or SELL. Each row is a separate valid execution delivered once, even when two rows have identical values.

A BUY adds its quantity and a SELL subtracts its quantity. Negative positions are allowed; a sell is never rejected for insufficient holdings.

Return [symbol, signedDecimalNetQuantity] for every symbol present in either table, including symbols whose result is zero. Sort rows by case-sensitive ASCII lexicographic symbol order. Quantities in the result use ordinary base10 notation without leading zeros or a plus sign; zero is "0". If both tables are empty, return an empty table.

Use signed 64-bit arithmetic for accumulated quantities. Do not modify either input table. Prices, open orders, profit/loss, pagination, retries, duplicate-event recovery and real external API implementation are outside this finite practice.

Function

calculateNetPositions(initialPositions: String[][], fills: String[][]) → String[][]

Examples

Example 1

initialPositions = [["A","10"],["B","-4"]]fills = [["A","BUY","3"],["A","SELL","5"],["C","SELL","2"]]return = [["A","8"],["B","-4"],["C","-2"]]

A finishes at10+3-5=8; B remains-4, and the previously absent C starts0 and becomes-2. Symbols are sorted.

Example 2

initialPositions = []fills = [["XYZ","BUY","5"],["XYZ","SELL","5"]]return = [["XYZ","0"]]

BUY and SELL cancel, but the encountered symbol must remain in the result with canonical zero.

Example 3

initialPositions = []fills = []return = []

Neither response contains a symbol, so return an empty table.

Constraints

0 <= initialPositions.length + fills.length <= 1000.
Each symbol contains 1 through 10 ASCII letters A-Z or a-z.
Initial quantities are signed decimal integers with magnitude at most 10^9.
Fill quantities are positive decimal integers from 1 through 10^9.
All rows have the stated shape and valid values. Initial symbols are unique; execution rows are distinct events and are processed once.
Net quantities fit signed 64-bit integers; their magnitude is at most 10^12.