LESSON 387 OF 415 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: grep v2 — Case-Insensitive Match in Swift

Practice

Build the -i flag of the Unix grep command. Given a list of lines and a search pattern, return all lines that contain pattern as a substring, ignoring letter case. Return the matching lines joined by newline characters (\n).

Function signature:

func grepCaseInsensitive(_ lines: [String], _ pattern: String) -> String

Example:

Input:
pattern = "ERR"
lines = ["Error: 1", "ok"]

Output: "Error: 1"

When printed:
Error: 1

The matching is case-insensitive but the original line (preserving its original casing) is returned. If no lines match, return the empty string "". The lines contain only ASCII characters.

Lowercase the pattern once, then for each line check line.lowercased().contains(lowerPattern). Append the ORIGINAL line on a hit.

The full solution:

class Solution {
    func grepCaseInsensitive(_ lines: [String], _ pattern: String) -> String {
        var result = [String]()
        let lowerPattern = pattern.lowercased()
        for line in lines {
            if line.lowercased().contains(lowerPattern) {
                result.append(line)
            }
        }
        return result.joined(separator: "\n")
    }
}

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CLI Tool: grep v2 — Case-Insensitive Match in Swift

Grep V2 in Swift