LESSON 611 OF 679 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: head v1 — First 10 Lines

Practice

Build a tiny version of the Unix head command. Given a list of lines, return the first 10 lines joined by newline characters (\n). If the input has fewer than 10 lines, return all of them. If there are no lines at all, return the empty string.

Function signature:

fn head(lines: Vec<String>) -> String

Example:

Input: lines = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m"]

Output: "a\nb\nc\nd\ne\nf\ng\nh\ni\nj"

When printed:
a
b
c
d
e
f
g
h
i
j

Compute the end index, capping it at lines.len() so a short input never panics. Then slice the vector and call join("\n") — Rust string slices have a built-in join.

Compute let end = lines.len().min(10), then return lines[0..end].join("\n").

The full solution:

impl Solution {
    fn head(lines: Vec<String>) -> String {
        let end = lines.len().min(10);
        lines[0..end].join("\n")
    }
}

STEP 1 OF 2

Guided

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