LESSON 621 OF 674 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: uniq v3 — Duplicates Only

Practice

Build a version of the Unix uniq -d command. Given a list of lines, output only the values whose adjacent run length is greater than one — i.e. lines that actually repeat back-to-back. Each surviving value is printed once (no count, just the value), joined by \n.

Function signature:

public string UniqDups(List<string> lines)

Example:

Input: lines = ["a", "a", "b", "c", "c", "c"]

Output: "a\nc"

When printed:
a
c

The run of "a"s has length 2 and the run of "c"s has length 3, so both survive. The single "b" is dropped.

Track prev and count. When the line changes (or after the loop), flush prev only if count > 1. Compare strings with ==, then join the survivors with string.Join.

if (count > 1) {
    result.Add(prev);
}

The full solution:

class Solution {
    public string UniqDups(List<string> lines) {
        List<string> result = new List<string>();
        int count = 0;
        string prev = "";
        for (int i = 0; i < lines.Count; i++) {
            if (count > 0 && lines[i] == prev) {
                count++;
            } else {
                if (count > 1) {
                    result.Add(prev);
                }
                prev = lines[i];
                count = 1;
            }
        }
        if (count > 1) {
            result.Add(prev);
        }
        return string.Join("\n", result);
    }
}

STEP 1 OF 13

Guided

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