Compress String by Character Count

Compress string by character count

Scala

import scala.annotation.tailrec

// compress to list of tuples
def compress(str: String):List[(Char, Int)] = str match {
  case "" => Nil
  case _ => {
    val (x,xs) = str span (c => c == str.head)
    (str.head, x.length) :: compress(xs)
  }
}

// compress to string
def compressString(str: String):String = {
  val sb = new StringBuilder
  @tailrec def compress(s: String):Unit = {
    if (!s.isEmpty) {
      val (x,xs) = s span (c => c == s.head)
      sb.append(s.head)
      sb.append(x.length.toString)
      compress(xs)
    }
  }
  compress(str)
  sb.toString
}

// compress in-place using char array
def compressInPlace(ch: Array[Char]):Unit = {
  var prev = ch.head
  var count = 1
  var write = 0
  for (c <- ch.tail) {
    c match {
      case c if c == prev => count += 1
      case _ => {
        ch(write) = prev
        if (count > 1) {
          for (j <- count.toString) {
            ch(write+1) = j
            write += 1
          }
        }
        write += 1
        count = 1
        prev = c
      }
    }
  }
  ch(write) = prev
  if (count > 1) ch(write+1) = count.toChar
  ch(write+1) = '\0'
}


// initialize string
val s = "aabccccccccccccccccccccccccccccccccccccccccccaaad"

compress(s)

compressString(s)

val ch = Array.fill(50){' '}
for (i <- 0 until s.length) {
  ch(i) = s(i)
}
compressInPlace(ch)
ch.mkString("").substring(0,ch.indexOf('\0'))

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