How should I practice Recent Metrics by Name and Tags?

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Problem · Design

Recent Metrics by Name and Tags

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Problem statement

Implement an in-memory metrics database. Process the rows of operations in order, starting with an empty database.

["RECORD", name, timestamp, value, tag1, ...] stores one metric. Each tag is written as key=value.
["SEARCH", name, n, tag1, ...] returns the most recent matching metrics. A stored metric matches when its name is equal and it contains every query tag with the same value; it may contain additional tags.

For each operation, append one row to the result. A RECORD row produces ["null"]. A SEARCH row contains up to n matching metrics ordered by descending timestamp, with later RECORD operations first when timestamps tie.

Encode each returned metric as name|timestamp|value|tags. In that encoding, sort its key=value tags lexicographically and join them with commas. A metric with no tags has an empty suffix after the final |. If fewer than n metrics match, return all of them; if none match or n is zero, return an empty row.

Function

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

Examples

Example 1

operations = [["RECORD","cpu","10","7","host=a","zone=west"],["RECORD","cpu","12","9","host=a"],["SEARCH","cpu","2","host=a"]]return = [["null"],["null"],["cpu|12|9|host=a","cpu|10|7|host=a,zone=west"]]

Both stored CPU metrics contain host=a. Timestamp 12 comes first, and the older metric may have the additional zone tag.

Example 2

operations = [["RECORD","latency","20","4","region=us"],["RECORD","latency","20","8","region=us","tier=api"],["SEARCH","latency","5","region=us"]]return = [["null"],["null"],["latency|20|8|region=us,tier=api","latency|20|4|region=us"]]

The two matching metrics have equal timestamps, so the metric recorded later is returned first. Its tags are sorted in the encoded record.

Example 3

operations = [["RECORD","cpu","1","5","host=a"],["SEARCH","memory","3","host=a"],["SEARCH","cpu","0"]]return = [["null"],[],[]]

The name memory has no stored metrics, and a limit of zero also returns an empty result row.

Constraints

1 <= operations.length <= 100.
Every operation begins with RECORD or SEARCH and follows the row shape in the statement.
Names, tag keys, and tag values contain 1 to 20 lowercase English letters, digits, or underscores.
Each row contains at most 20 tags with distinct keys.
0 <= timestamp <= 10^9 and -10^9 <= value <= 10^9.
0 <= n <= 100.