LESSON 398 OF 414 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: tr v2 — Set Translation in Scala

Practice

Build a more powerful version of the Unix tr command. Given a list of lines and two equal-length strings set1 and set2, replace every character in each line that appears in set1 at index i with set2[i]. Characters not in set1 are unchanged. Return the lines joined by newline characters (\n).

Notes: set1 and set2 have the same length, contain only ASCII characters, and set1 has no repeated character. Characters are taken literally: there are no ranges like a-z. All replacements happen at once, so set1 = "ab", set2 = "ba" swaps the two letters. Lines may be empty.

Function signature:

def tr(lines: List[String], set1: String, set2: String): String

Example:

Input: lines = ["banana", "cherry"], set1 = "abc", set2 = "ABC"

Output: "BAnAnA\nCherry"

When printed:
BAnAnA
Cherry

Build a HashMap[Char, Char] from each char in set1 to the matching char in set2. Then walk each line and use map.getOrElse(ch, ch) to translate.

val map = scala.collection.mutable.HashMap[Char, Char]()
for (i <- 0 until set1.length) {
    map(set1(i)) = set2(i)
}
// per char: map.getOrElse(ch, ch)

The full solution:

class Solution {
    def tr(lines: List[String], set1: String, set2: String): String = {
        val map = scala.collection.mutable.HashMap[Char, Char]()
        for (i <- 0 until set1.length) {
            map(set1(i)) = set2(i)
        }
        val result = scala.collection.mutable.ArrayBuffer[String]()
        for (line <- lines) {
            val sb = new StringBuilder()
            for (ch <- line) {
                sb.append(map.getOrElse(ch, ch))
            }
            result += sb.toString()
        }
        return result.mkString("\n")
    }
}

STEP 1 OF 10

Guided

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CLI Tool: tr v2 — Set Translation in Scala

Tr V2 in Scala