LESSON 385 OF 413 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: grep v2 — Case-Insensitive Match in C#

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.ToLower().Contains(lowerPattern). Add the ORIGINAL line on a hit.

The full solution:

class Solution {
    public string GrepCaseInsensitive(List<string> lines, string pattern) {
        List<string> result = new List<string>();
        string lowerPattern = pattern.ToLower();
        foreach (string line in lines) {
            if (line.ToLower().Contains(lowerPattern)) {
                result.Add(line);
            }
        }
        return string.Join("\n", result);
    }
}

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CLI Tool: grep v2 — Case-Insensitive Match in C#

Grep V2 in C#