LESSON 376 OF 414 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: cat v4 — Concatenate Multiple Files in Scala

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:

def 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 buffer of String with a nested loop, preserving order. Then return flat.mkString("\n").

val flat = scala.collection.mutable.ArrayBuffer[String]()
for (fileLines <- allLines) {
    for (line <- fileLines) {
        flat += line
    }
}
return flat.mkString("\n")

The full solution:

class Solution {
    def concatCat(allLines: List[List[String]]): String = {
        val flat = scala.collection.mutable.ArrayBuffer[String]()
        for (fileLines <- allLines) {
            for (line <- fileLines) {
                flat += line
            }
        }
        return flat.mkString("\n")
    }
}

STEP 1 OF 5

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CLI Tool: cat v4 — Concatenate Multiple Files in Scala

Cat V4 in Scala