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Extensible Grep Line Filter

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Problem statement

A text file is serialized as the array lines. Return every original line selected by a simplified grep command, preserving file order and duplicate lines.

A line initially matches when it contains pattern as a contiguous substring. The unique flags in flags may appear in either order:

-i makes substring matching case-insensitive for ASCII letters.
-v inverts the final match decision.

An empty pattern matches every line before optional inversion. Return original line text without normalization.

Function

grepLines(lines: String[], pattern: String, flags: String[]) → String[]

Examples

Example 1

lines = ["error: disk full","INFO ready","network error"]pattern = "error"flags = []return = ["error: disk full","network error"]

The first and third lines contain the case-sensitive substring error.

Example 2

lines = ["Error","all good","ERROR again"]pattern = "error"flags = ["-i"]return = ["Error","ERROR again"]

The -i flag ignores ASCII letter case while returned lines keep their original text.

Example 3

lines = ["warn","ok","WARN"]pattern = "warn"flags = ["-v","-i"]return = ["ok"]

Case-insensitive matching selects the two warning lines, then -v returns their complement.

Constraints

0 <= lines.length <= 10000.
0 <= lines[i].length <= 500.
0 <= pattern.length <= 100.
0 <= flags.length <= 2.
Every line and pattern contains printable ASCII characters.
flags contains unique values chosen from -i and -v.