import Foundation
/* ---------------------------------------------------------
Compress: turn "aaabbcccc" into "a3b2c4"
This is run-length encoding (RLE)
--------------------------------------------------------- */
func compress(_ s: String) -> String {
if s.isEmpty {
return "" // Edge case: empty string
}
var out = "" // Result string
var count = 1 // Count of repeated characters
let chars = Array(s)
// Start from index 1 and compare with previous character
for i in 1...chars.count {
// If still repeating the same character, increase count
if i < chars.count && chars[i] == chars[i - 1] {
count += 1
} else {
// Character changed OR reached end of string
out.append(chars[i - 1]) // Add the character
out.append(String(count)) // Add how many times it repeated
count = 1 // Reset counter
}
}
return out
}
/* ---------------------------------------------------------
Decompress: turn "a3b2c4" into "aaabbcccc"
Reads a letter, then reads digits, expands them.
--------------------------------------------------------- */
func decompress(_ s: String) -> String {
var out = "" // Result string
var currentChar: Character? // The character being processed
var number = "" // Digits representing the count
for c in s {
if c.isLetter { // Found a letter
// If we already have a previous letter + number, expand it
if let ch = currentChar, !number.isEmpty {
if let count = Int(number) {
out.append(String(repeating: String(ch), count: count))
}
}
currentChar = c // Start new character
number = "" // Reset number buffer
} else if c.isNumber { // Found a digit
number.append(c) // Build multi-digit number
}
}
// Handle the last character + number pair
if let ch = currentChar, !number.isEmpty {
if let count = Int(number) {
out.append(String(repeating: String(ch), count: count))
}
}
return out
}
func main() {
let s = "wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww"
let c = compress(s)
let d = decompress(c)
print("Original: \(s)")
print("Compressed: \(c)")
print("Decompressed: \(d)")
}
main()
/*
run:
Original: wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww
Compressed: w12b1w10b3w6c4w12
Decompressed: wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww
*/
