LESSON 392 OF 414 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: uniq v4 — Loners Only in Scala

Practice

Build a version of the Unix uniq -u command. Given a list of lines, output only the values whose adjacent run length is exactly one — i.e. lines that did NOT repeat back-to-back. Surviving values are joined by \n.

Function signature:

def uniqOnce(lines: Array[String]): String

Example:

Input: lines = ["a", "a", "b", "c", "c", "c"]

Output: "b"

When printed:
b

The two "a"s and the three "c"s are dropped because their runs are longer than 1. Only the lone "b" survives.

Track prev and count. When the line changes (or after the loop), flush prev only if count == 1.

if (count == 1) {
    result += prev
}

In Scala, == compares string values directly.

The full solution:

class Solution {
    def uniqOnce(lines: Array[String]): String = {
        val result = scala.collection.mutable.ArrayBuffer[String]()
        var count = 0
        var prev: String = null
        for (i <- 0 until lines.length) {
            if (count > 0 && lines(i) == prev) {
                count += 1
            } else {
                if (count == 1) {
                    result += prev
                }
                prev = lines(i)
                count = 1
            }
        }
        if (count == 1) {
            result += prev
        }
        return result.mkString("\n")
    }
}

STEP 1 OF 13

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CLI Tool: uniq v4 — Loners Only in Scala

Uniq V4 in Scala