import scala.collection.mutable.StringBuilder
/* ---------------------------------------------------------
Compress: turn "aaabbcccc" into "a3b2c4"
This is run-length encoding (RLE)
--------------------------------------------------------- */
def compress(s: String): String = {
if (s.isEmpty)
return "" // Edge case: empty string
val out = new StringBuilder() // Result string
var count = 1 // Count of repeated characters
// Start from index 1 and compare with previous character
for (i <- 1 to s.length) {
// If still repeating the same character, increase count
if (i < s.length && s(i) == s(i - 1)) {
count += 1
} else {
// Character changed OR reached end of string
out.append(s(i - 1)) // Add the character
out.append(count.toString) // Add how many times it repeated
count = 1 // Reset counter
}
}
out.toString()
}
/* ---------------------------------------------------------
Decompress: turn "a3b2c4" into "aaabbcccc"
Reads a letter, then reads digits, expands them.
--------------------------------------------------------- */
def decompress(s: String): String = {
val out = new StringBuilder() // Result string
var currentChar: Option[Char] = None // The character being processed
val number = new StringBuilder() // Digits representing the count
for (c <- s) {
if (c.isLetter) { // Found a letter
// If we already have a previous letter + number, expand it
currentChar.foreach { ch =>
if (number.nonEmpty) {
val count = number.toString.toInt
out.append(ch.toString * count)
}
}
currentChar = Some(c) // Start new character
number.clear() // Reset number buffer
} else if (c.isDigit) { // Found a digit
number.append(c) // Build multi-digit number
}
}
// Handle the last character + number pair
currentChar.foreach { ch =>
if (number.nonEmpty) {
val count = number.toString.toInt
out.append(ch.toString * count)
}
}
out.toString()
}
@main def main(): Unit = {
val s = "wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww"
val c = compress(s)
val d = decompress(c)
println(s"Original: $s")
println(s"Compressed: $c")
println(s"Decompressed: $d")
}
/*
run:
Original: wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww
Compressed: w12b1w10b3w6c4w12
Decompressed: wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww
*/
