LESSON 377 OF 415 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: cat v4 — Concatenate Multiple Files in Swift

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:

func concatCat(_ allLines: [[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 [String] with a nested loop, preserving order. Then return flat.joined(separator: "\n").

var flat: [String] = []
for fileLines in allLines {
    for line in fileLines {
        flat.append(line)
    }
}
return flat.joined(separator: "\n")

The full solution:

class Solution {
    func concatCat(_ allLines: [[String]]) -> String {
        var flat: [String] = []
        for fileLines in allLines {
            for line in fileLines {
                flat.append(line)
            }
        }
        return flat.joined(separator: "\n")
    }
}

STEP 1 OF 5

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CLI Tool: cat v4 — Concatenate Multiple Files in Swift

Cat V4 in Swift