java字符串压缩算法代码

以下是Java中几种字符串压缩算法的示例代码：

RLE算法：

public static String compressRLE(String str) {
    StringBuilder result = new StringBuilder();
    int count = 1;
    char prev = str.charAt(0);
    for (int i = 1; i < str.length(); i++) {
        char current = str.charAt(i);
        if (current == prev) {
            count++;
        } else {
            result.append(count).append(prev);
            count = 1;
            prev = current;
        }
    }
    result.append(count).append(prev);
    return result.toString();
}

LZW算法：

public static String compressLZW(String str) {
    Map<String, Integer> dictionary = new HashMap<>();
    for (int i = 0; i < 256; i++) {
        dictionary.put("" + (char) i, i);
    }
    String current = "";
    List<Integer> codes = new ArrayList<>();
    for (char c : str.toCharArray()) {
        String next = current + c;
        if (dictionary.containsKey(next)) {
            current = next;
        } else {
            codes.add(dictionary.get(current));
            dictionary.put(next, dictionary.size());
            current = "" + c;
        }
    }
    if (!current.equals("")) {
        codes.add(dictionary.get(current));
    }
    StringBuilder result = new StringBuilder();
    for (int code : codes) {
        result.append(code).append(" ");
    }
    return result.toString();
}

Huffman编码算法：

public static String compressHuffman(String str) {
    Map<Character, Integer> frequencies = new HashMap<>();
    for (char c : str.toCharArray()) {
        frequencies.put(c, frequencies.getOrDefault(c, 0) + 1);
    }
    PriorityQueue<Node> queue = new PriorityQueue<>();
    for (Map.Entry<Character, Integer> entry : frequencies.entrySet()) {
        queue.offer(new Node(entry.getKey(), entry.getValue()));
    }
    while (queue.size() > 1) {
        Node left = queue.poll();
        Node right = queue.poll();
        Node parent = new Node('\0', left.frequency + right.frequency, left, right);
        queue.offer(parent);
    }
    Map<Character, String> codes = new HashMap<>();
    buildCodes(codes, queue.peek(), "");
    StringBuilder result = new StringBuilder();
    for (char c : str.toCharArray()) {
        result.append(codes.get(c));
    }
    return result.toString();
}

private static void buildCodes(Map<Character, String> codes, Node node, String code) {
    if (node.left == null && node.right == null) {
        codes.put(node.character, code);
    } else {
        buildCodes(codes, node.left, code + "0");
        buildCodes(codes, node.right, code + "1");
    }
}

private static class Node implements Comparable<Node> {
    char character;
    int frequency;
    Node left;
    Node right;

    Node(char character, int frequency) {
        this.character = character;
        this.frequency = frequency;
    }

    Node(char character, int frequency, Node left, Node right) {
        this.character = character;
        this.frequency = frequency;
        this.left = left;
        this.right = right;
    }

    @Override
    public int compareTo(Node o) {
        return frequency - o.frequency;
    }
}

以上代码仅供参考，实际使用时可能需要根据具体需求进行修改和优化。