LESSON 382 OF 410 · PROJECTS: COMMAND-LINE TOOLS

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

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:

public String grepCaseInsensitive(List<String> lines, String pattern)

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.toLowerCase().contains(lowerPattern). Push the ORIGINAL line on a hit.

The full solution:

class Solution {
    public String grepCaseInsensitive(List<String> lines, String pattern) {
        List<String> result = new ArrayList<>();
        String lowerPattern = pattern.toLowerCase();
        for (String line : lines) {
            if (line.toLowerCase().contains(lowerPattern)) {
                result.add(line);
            }
        }
        return String.join("\n", result);
    }
}

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

Grep V2 in Java