LESSON 376 OF 414 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: cat v4 — Concatenate Multiple Files in Kotlin

Practice

The real cat command can take many files as arguments and prints them one after another. Build that behavior. Given a list of "files" where each file is itself a list of lines, flatten all lines in order and join them with newlines.

A file can be empty (it adds no lines), and the list can hold no files at all; the result is then an empty string.

Function signature:

fun concatCat(allLines: List<List<String>>): String

Example:

Input: allLines = [["hello", "world"], ["foo", "bar", "baz"]]

Output: "hello\nworld\nfoo\nbar\nbaz"

When printed:
hello
world
foo
bar
baz

Build a flat MutableList<String> with a nested loop, preserving order. Then return flat.joinToString("\n").

val flat = mutableListOf<String>()
for (fileLines in allLines) {
    for (line in fileLines) {
        flat.add(line)
    }
}
return flat.joinToString("\n")

The full solution:

class Solution {
    fun concatCat(allLines: List<List<String>>): String {
        val flat = mutableListOf<String>()
        for (fileLines in allLines) {
            for (line in fileLines) {
                flat.add(line)
            }
        }
        return flat.joinToString("\n")
    }
}

STEP 1 OF 5

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CLI Tool: cat v4 — Concatenate Multiple Files in Kotlin

Cat V4 in Kotlin