Parse logs and count error codes

Q: Parse logs and count error codes

This is a Coding & Algorithms interview question from Nuro for Software Engineer roles. View the full question and solution on PracHub.

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Question

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You are given application log lines. Each line is expected to follow this format:

[LEVEL] timestamp, eventName, errorCode, text

LEVEL is a single character such as I , W , E inside square brackets (e.g., [I] ).
Fields after the level are separated by commas.
text may contain arbitrary characters (assume it does not contain a newline).

Task

Write a Python function that parses a list of log lines and returns the count of each errorCode.

Input

A list of strings lines , where each string is one log line.

Output

A dictionary/map from errorCode (string) to its occurrence count (integer).

Requirements / Edge cases

Trim extra whitespace around comma-separated fields.
Ignore lines that do not match the expected format (do not crash).
Treat errorCode as a string (e.g., "404" , "E123" ).

Example

Input:

[I] 2026-01-01T00:00:00Z, Login, E123, user not found
[W] 2026-01-01T00:00:01Z, Login, E123, retry
[E] 2026-01-01T00:00:02Z, Payment, P007, declined

Output:

{ "E123": 2, "P007": 1 }