Method compress

src/main/java/com/thealgorithms/compression/LZ78.java:68–105

Compresses the input text using the LZ78 algorithm. @param text The input string to compress. Must not be null. @return A list of Token objects representing the compressed data.

(String text)

     * @return A list of {@link Token} objects representing the compressed data.
     */
    public static List<Token> compress(String text) {
        if (text == null || text.isEmpty()) {
            return new ArrayList<>();
        }

        List<Token> compressedOutput = new ArrayList<>();
        TrieNode root = new TrieNode();
        int nextDictionaryIndex = 1;

        TrieNode currentNode = root;
        int lastMatchedIndex = 0;

        for (int i = 0; i < text.length(); i++) {
            char currentChar = text.charAt(i);

            if (currentNode.children.containsKey(currentChar)) {
                currentNode = currentNode.children.get(currentChar);
                lastMatchedIndex = currentNode.index;
            } else {
                // Output: (index of longest matching prefix, current character)
                compressedOutput.add(new Token(lastMatchedIndex, currentChar));

                TrieNode newNode = new TrieNode();
                newNode.index = nextDictionaryIndex++;
                currentNode.children.put(currentChar, newNode);

                currentNode = root;
                lastMatchedIndex = 0;
            }
        }

        // Handle remaining phrase at end of input
        if (currentNode != root) {
            compressedOutput.add(new Token(lastMatchedIndex, END_OF_STREAM));
        }

        return compressedOutput;
    }

    /**
     * Decompresses a list of LZ78 tokens back into the original string.