import java.lang.Character;
import java.lang.Integer;
import java.lang.String;
import java.lang.StringBuilder;
import java.util.Arrays;
/** ---------------------------------------------------------
Compress: turn "aaabbcccc" into "a3b2c4"
This is run-length encoding (RLE)
--------------------------------------------------------- */
public class RLE {
public static String compress(String s) {
if (s.isEmpty()) return ""; // Edge case: empty string
StringBuilder out = new StringBuilder(); // Result string
int count = 1; // Count of repeated characters
// Start from index 1 and compare with previous character
for (int i = 1; i <= s.length(); i++) {
// If still repeating the same character, increase count
if (i < s.length() && s.charAt(i) == s.charAt(i - 1)) {
count++;
}
else {
// Character changed OR reached end of string
out.append(s.charAt(i - 1)); // Add the character
out.append(count); // Add how many times it repeated
count = 1; // Reset counter
}
}
return out.toString();
}
/** ---------------------------------------------------------
Decompress: turn "a3b2c4" into "aaabbcccc"
Reads a letter, then reads digits, expands them.
--------------------------------------------------------- */
public static String decompress(String s) {
StringBuilder out = new StringBuilder(); // Result string
char currentChar = '\0'; // The character being processed
StringBuilder number = new StringBuilder(); // Digits representing the count
for (char c : s.toCharArray()) {
if (Character.isLetter(c)) { // Found a letter
// If we already have a previous letter + number, expand it
if (currentChar != '\0' && number.length() > 0) {
int count = Integer.parseInt(number.toString());
out.append(String.valueOf(currentChar).repeat(count));
}
currentChar = c; // Start new character
number.setLength(0); // Reset number buffer
}
else if (Character.isDigit(c)) { // Found a digit
number.append(c); // Build multi-digit number
}
}
// Handle the last character + number pair
if (currentChar != '\0' && number.length() > 0) {
int count = Integer.parseInt(number.toString());
out.append(String.valueOf(currentChar).repeat(count));
}
return out.toString();
}
public static void main(String[] args) {
String s = "wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww";
String c = compress(s);
String d = decompress(c);
System.out.println("Original: " + s);
System.out.println("Compressed: " + c);
System.out.println("Decompressed: " + d);
}
}
/*
run:
Original: wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww
Compressed: w12b1w10b3w6c4w12
Decompressed: wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww
*/
