Method compress

src/main/java/com/thealgorithms/compression/LZW.java:57–89

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

(String uncompressed)

     * list if the input is null or empty.
     */
    public static List<Integer> compress(String uncompressed) {
        if (uncompressed == null || uncompressed.isEmpty()) {
            return new ArrayList<>();
        }

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

        String w = "";
        List<Integer> result = new ArrayList<>();
        for (char c : uncompressed.toCharArray()) {
            String wc = w + c;
            if (dictionary.containsKey(wc)) {
                // If the new string is in the dictionary, extend the current string
                w = wc;
            } else {
                // Otherwise, output the code for the current string
                result.add(dictionary.get(w));
                // Add the new string to the dictionary
                dictionary.put(wc, dictSize++);
                // Start a new current string
                w = "" + c;
            }
        }

        // Output the code for the last remaining string
        result.add(dictionary.get(w));
        return result;
    }

    /**
     * Decompresses a list of integers back into a string using the LZW algorithm.