LZ78 压缩算法的 Java 实现

r囧r小猫 2022-10-21 12:56 197阅读 0赞

### 文章目录 ###

*  LZ78 压缩算法的 Java 实现
 *   *   *   *  1、压缩算法的实现
             *  2、解压缩算法的实现
             *  3、测试和使用
             *  4、Python 版本的实现代码

# LZ78 压缩算法的 Java 实现 #

--------------------

#### 1、压缩算法的实现 ####

通过多路搜索树提高检索速度

package com.wretchant.lz78;
    
    import java.util.*;
    
    /** 多路英文单词查找树 */
    class Trie { 
        private TrieNode root;
    
        public Trie() { 
            root = new TrieNode();
            root.wordEnd = false;
        }
    
        public void insert(String word) { 
            TrieNode node = root;
            for (int i = 0; i < word.length(); i++) { 
                Character c = word.charAt(i);
                if (!node.childdren.containsKey(c)) { 
                    node.childdren.put(c, new TrieNode());
                }
                node = node.childdren.get(c);
            }
            node.wordEnd = true;
        }
    
        public boolean search(String word) { 
            TrieNode node = root;
            for (int i = 0; i < word.length(); i++) { 
                Character c = word.charAt(i);
                if (!node.childdren.containsKey(c)) { 
                    return false;
                }
                node = node.childdren.get(c);
            }
            return node.wordEnd;
        }
    
    }
    
    class TrieNode { 
        Map<Character, TrieNode> childdren;
        boolean wordEnd;
    
        public TrieNode() { 
            childdren = new HashMap<Character, TrieNode>();
            wordEnd = false;
        }
    }
    
    /** 编码表 */
    class Output { 
        private Integer index;
        private Character character;
    
        Output(Integer index, Character character) { 
            this.index = index;
            this.character = character;
        }
    
        public Integer getIndex() { 
            return index;
        }
    
        public Character getCharacter() { 
            return character;
        }
    }
    
    class LZencode { 
        @FunctionalInterface
        interface Encode { 
            List<Output> encode(String message);
        }
    
        /** 构建多路搜索树 */
        static Trie buildTree(Set<String> keys) { 
            Trie trie = new Trie();
            keys.forEach(trie::insert);
            return trie;
        }
    
        public static final Encode ENCODE = message -> { 
            // 构建压缩后的编码表
            List<Output> outputs = new ArrayList<>();
            Map<String, Integer> treeDict = new HashMap<>();
            int mLen = message.length();
            int i = 0;
    
            while (i < mLen) { 
                Set<String> keySet = treeDict.keySet();
                // 生成多路搜索树
                Trie trie = buildTree(keySet);
                char messageI = message.charAt(i);
                String messageIStr = String.valueOf(messageI);
                // 使用多路树进行搜索
                if (!trie.search(messageIStr)) { 
                    outputs.add(new Output(0, messageI));
                    treeDict.put(messageIStr, treeDict.size() + 1);
                    i++;
                } else if (i == mLen - 1) { 
                    outputs.add(new Output(treeDict.get(messageIStr), ' '));
                    i++;
                } else { 
                    for (int j = i + 1; j < mLen; j++) { 
                        String substring = message.substring(i, j + 1);
                        String str = message.substring(i, j);
                        // 使用多路树进行搜索
                        if (!trie.search(substring)) { 
                            outputs.add(new Output(treeDict.get(str), message.charAt(j)));
                            treeDict.put(substring, treeDict.size() + 1);
                            i = j + 1;
                            break;
                        }
                        if (j == mLen - 1) { 
                            outputs.add(new Output(treeDict.get(substring), ' '));
                            i = j + 1;
                        }
                    }
                }
            }
            return outputs;
        };
    
    
    }

#### 2、解压缩算法的实现 ####

package com.wretchant.lz78;
    
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    
    public class LZdecode { 
    
    
        @FunctionalInterface
        interface Decode { 
            /** @param outputs 编码表 @return 解码后的字符串 */
            String decode(List<Output> outputs);
        }
    
        /** 根据编码表进行解码 */
        public static final Decode DECODE = (List<Output> outputs) -> { 
            StringBuilder unpacked = new StringBuilder();
            Map<Integer, String> treeDict = new HashMap<>();
    
            for (Output output : outputs) { 
                Integer index = output.getIndex();
                Character character = output.getCharacter();
                if (index == 0) { 
                    unpacked.append(character);
                    treeDict.put(treeDict.size() + 1, character.toString());
                    continue;
                }
                String term = "" + treeDict.get(index) + character;
                unpacked.append(term);
                treeDict.put(treeDict.size() + 1, term);
    
            }
    
            return unpacked.toString();
        };
    }

#### 3、测试和使用 ####

package com.wretchant.lz78;
    
    import java.io.InputStream;
    import java.util.List;
    import java.util.Scanner;
    import java.util.function.ToIntFunction;
    
    public class LZpack { 
    
        public static final ToIntFunction<List<Output>> DICT_PRINT = outputs -> { 
            outputs.forEach(output -> { 
                System.out.println("index :" + output.getIndex() + " char :" + output.getCharacter());
            });
            return 1;
        };
    
        public static void main(String[] args) { 
    
            Scanner scanner = new Scanner(System.in);
            System.out.println("Please input text ");
            String input = scanner.nextLine();
    
            LZencode.Encode encode = LZencode.ENCODE;
            List<Output> outputs = encode.encode(input);
            DICT_PRINT.applyAsInt(outputs);
        }
    }

测试结果如下  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzE1MDcxMjYz_size_16_color_FFFFFF_t_70]

#### 4、Python 版本的实现代码 ####

def compress(message):
        tree_dict, m_len, i = { }, len(message), 0
        while i < m_len:
            # case I
            if message[i] not in tree_dict.keys():
                yield (0, message[i])
                tree_dict[message[i]] = len(tree_dict) + 1
                i += 1
            # case III
            elif i == m_len - 1:
                yield (tree_dict.get(message[i]), '')
                i += 1
            else:
                for j in range(i + 1, m_len):
                    # case II
                    if message[i:j + 1] not in tree_dict.keys():
                        yield (tree_dict.get(message[i:j]), message[j])
                        tree_dict[message[i:j + 1]] = len(tree_dict) + 1
                        i = j + 1
                        break
                    # case III
                    elif j == m_len - 1:
                        yield (tree_dict.get(message[i:j + 1]), '')
                        i = j + 1
    
    
    def uncompress(packed):
        unpacked, tree_dict = '', { }
        for index, ch in packed:
            if index == 0:
                unpacked += ch
                tree_dict[len(tree_dict) + 1] = ch
            else:
                term = tree_dict.get(index) + ch
                unpacked += term
                tree_dict[len(tree_dict) + 1] = term
        return unpacked
    
    
    if __name__ == '__main__':
        messages = ['ABBCBCABABCAABCAAB', 'BABAABRRRA', 'AAAAAAAAA']
        for m in messages:
            pack = compress(m)
            unpack = uncompress(pack)
            print(unpack == m)

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzE1MDcxMjYz_size_16_color_FFFFFF_t_70]: /images/20221021/31a4d03f669a4943b1e362ac4bc5d17e.png