LESSON 390 OF 414 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: uniq v2 — Count Adjacent Runs in Scala

Practice

Build a version of the Unix uniq -c command. Given a list of lines, collapse each run of adjacent duplicates into a single output line that shows the run's count followed by the value.

Each output line is formatted as "%7d %s".format(count, value): a 7-character right-aligned count, a single space, then the line value. Join all output lines with \n.

Function signature:

def uniqCount(lines: List[String]): String

Example:

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

Output (when printed):
      2 a
      1 b
      3 c

The first run is two "a"s, then a single "b", then three "c"s — three output lines.

Track var prev and var count. When a NEW value comes in (or you reach end), flush the previous run with "%7d %s".format(count, prev) and reset.

Don't forget to flush AFTER the loop too. Use == for the string comparison.

if (count > 0 && lines(i) == prev) {
    count += 1
} else {
    if (count > 0) {
        result += "%7d %s".format(count, prev)
    }
    prev = lines(i)
    count = 1
}

The full solution:

class Solution {
    def uniqCount(lines: List[String]): String = {
        val result = scala.collection.mutable.ArrayBuffer[String]()
        var count = 0
        var prev = ""
        for (i <- lines.indices) {
            if (count > 0 && lines(i) == prev) {
                count += 1
            } else {
                if (count > 0) {
                    result += "%7d %s".format(count, prev)
                }
                prev = lines(i)
                count = 1
            }
        }
        if (count > 0) {
            result += "%7d %s".format(count, prev)
        }
        return result.mkString("\n")
    }
}

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CLI Tool: uniq v2 — Count Adjacent Runs in Scala

Uniq V2 in Scala