LESSON 376 OF 410 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: head v4 — Negative n drops the tail in JavaScript

Practice

Same signature as v2/v3, but now n may be negative. Real head -n -K prints all lines except the last K. So when n < 0 return all lines except the last |n|; when n ≥ 0 behave exactly like v3 (return the first n, capped at the input length). If |n| is at least the number of lines, nothing is left, so return the empty string.

Function signature:

head(lines, n)

Example (negative n):

Input: lines = ["a", "b", "c", "d", "e"], n = -2

Output: "a\nb\nc"

When printed:
a
b
c

JavaScript's slice(0, n) already does the right thing for both signs. A negative end index means "stop that many from the end".

The full solution is the same one-liner from v2/v3:

class Solution {
    head(lines, n) {
        return lines.slice(0, n).join("\n");
    }
}

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Guided

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CLI Tool: head v4 — Negative n drops the tail in JavaScript

Head V4 in JavaScript