Method decompress

src/main/java/com/thealgorithms/compression/LZW.java:99–135

Decompresses a list of integers back into a string using the LZW algorithm. @param compressed A list of integers representing the compressed data. Can be null. @return The original, uncompressed string. Returns an empty string if the input is null or empty.

(List<Integer> compressed)

     * input is null or empty.
     */
    public static String decompress(List<Integer> compressed) {
        if (compressed == null || compressed.isEmpty()) {
            return "";
        }

        // Initialize dictionary with single characters (ASCII 0-255)
        int dictSize = 256;
        Map<Integer, String> dictionary = new HashMap<>();
        for (int i = 0; i < dictSize; i++) {
            dictionary.put(i, "" + (char) i);
        }

        // Decompress the first code
        String w = "" + (char) (int) compressed.removeFirst();
        StringBuilder result = new StringBuilder(w);

        for (int k : compressed) {
            String entry;
            if (dictionary.containsKey(k)) {
                // The code is in the dictionary
                entry = dictionary.get(k);
            } else if (k == dictSize) {
                // Special case for sequences like "ababab"
                entry = w + w.charAt(0);
            } else {
                throw new IllegalArgumentException("Bad compressed k: " + k);
            }

            result.append(entry);

            // Add new sequence to the dictionary
            dictionary.put(dictSize++, w + entry.charAt(0));

            w = entry;
        }
        return result.toString();
    }
}