LESSON 388 OF 410 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: uniq v4 — Loners Only in JavaScript

Practice

Build a version of the Unix uniq -u command. Given a list of lines, output only the values whose adjacent run length is exactly one — i.e. lines that did NOT repeat back-to-back. Surviving values are joined by \n.

Function signature:

uniqOnce(lines)

Example:

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

Output: "b"

When printed:
b

The two "a"s and the three "c"s are dropped because their runs are longer than 1. Only the lone "b" survives.

Same scaffolding as uniq -d, but the filter flips: flush prev only when count === 1.

if (count === 1) {
    result.push(prev);
}

Don't forget to flush AFTER the loop too.

The full solution:

class Solution {
    uniqOnce(lines) {
        let result = [];
        let count = 0;
        let prev = null;
        for (let i = 0; i < lines.length; i++) {
            if (count > 0 && lines[i] === prev) {
                count++;
            } else {
                if (count === 1) {
                    result.push(prev);
                }
                prev = lines[i];
                count = 1;
            }
        }
        if (count === 1) {
            result.push(prev);
        }
        return result.join("\n");
    }
}

STEP 1 OF 13

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CLI Tool: uniq v4 — Loners Only in JavaScript

Uniq V4 in JavaScript