LESSON 397 OF 414 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: tr v1 — Single Char Swap in Scala

Practice

Build a tiny version of the Unix tr command. Given a list of lines and two single characters fromChar and toChar, replace every occurrence of fromChar with toChar in each line, then return the lines joined by newline characters (\n).

Notes: fromChar and toChar are single ASCII characters, taken literally (no escapes like \, no ranges). Upper and lower case are different characters. A line may be empty, and may not contain fromChar at all.

Function signature:

def tr(lines: Array[String], fromChar: String, toChar: String): String

Example:

Input: lines = ["banana", "apple"], fromChar = "a", toChar = "X"

Output: "bXnXnX\nXpple"

When printed:
bXnXnX
Xpple

Scala strings expose Java's replace(CharSequence, CharSequence), which swaps EVERY occurrence. Apply it to each line and accumulate.

The full solution:

class Solution {
    def tr(lines: Array[String], fromChar: String, toChar: String): String = {
        val result = scala.collection.mutable.ArrayBuffer[String]()
        for (line <- lines) {
            result += line.replace(fromChar, toChar)
        }
        return result.mkString("\n")
    }
}

STEP 1 OF 4

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CLI Tool: tr v1 — Single Char Swap in Scala

Tr V1 in Scala