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Optimized Character Trie Implemented in Java 8
There is a newer version: 2.1.0
/*
 * Copyright (c) 2019 by Andrew Charneski.
 *
 * The author licenses this file to you under the
 * Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance
 * with the License.  You may obtain a copy
 * of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package com.simiacryptus.text;

import com.simiacryptus.util.binary.BitInputStream;
import com.simiacryptus.util.binary.BitOutputStream;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.List;
import java.util.TreeMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * The type Char trie serializer.
 */
public class CharTrieSerializer {

  /**
   * Serialize byte [ ].
   *
   * @param charTrie the char trie
   * @return the byte [ ]
   */
  public byte[] serialize(CharTrie charTrie) {
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    try {
      try (BitOutputStream out = new BitOutputStream(buffer)) {
        int level = 0;
        while (serialize(charTrie.root(), out, level++) > 0) {
        }
      }
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
    return buffer.toByteArray();
  }

  private int serialize(TrieNode root, BitOutputStream out, int level) {
    AtomicInteger nodesWritten = new AtomicInteger(0);
    if (0 == level) {
      TreeMap children = root.getChildrenMap();
      try {
        int size = children.size();
        out.writeVarLong(size);
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
      children.forEach((token, child) -> {
        try {
          out.write(child.getChar());
          out.writeVarLong(null == child ? 0 : child.getCursorCount());
          nodesWritten.incrementAndGet();
        } catch (IOException e) {
          throw new RuntimeException(e);
        }
      });
    } else {
      root.streamDecendents(level).forEach(node -> {
        TrieNode godparent = node.godparent();
        Stream stream = godparent.getChildren().map(x -> x);
        TreeMap godchildren = godparent.getChildrenMap();
        Stream stream1 = node.getChildren().map(x -> x);
        TreeMap children = node.getChildrenMap();
        godchildren.forEach((token, godchild) -> {
          TrieNode child = children.get(token);
          try {
            if (null == child) {
              out.writeVarLong(0);
            } else {
              out.writeVarLong(child.getCursorCount());
            }
            nodesWritten.incrementAndGet();
          } catch (IOException e) {
            throw new RuntimeException(e);
          }
        });
      });
    }
    return nodesWritten.get();

  }

  /**
   * Deserialize char trie.
   *
   * @param bytes the bytes
   * @return the char trie
   */
  public CharTrie deserialize(byte[] bytes) {
    CharTrie trie = new CharTrie();
    BitInputStream in = new BitInputStream(new ByteArrayInputStream(bytes));
    int level = 0;
    while (deserialize(trie.root(), in, level++) > 0) {
    }
    trie.recomputeCursorDetails();
    return trie;
  }

  private int deserialize(TrieNode root, BitInputStream in, int level) {
    AtomicInteger nodesRead = new AtomicInteger(0);
    if (0 == level) {
      try {
        long numberOfChildren = in.readVarLong();
        TreeMap children = new TreeMap<>();
        for (int i = 0; i < numberOfChildren; i++) {
          char c = (char) in.read(16).toLong();
          long cnt = in.readVarLong();
          children.put(c, cnt);
          nodesRead.incrementAndGet();
        }
        root.writeChildren(children);
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    } else {
      root.streamDecendents(level).forEach(node -> {
        TrieNode godparent = node.godparent();
        List list = godparent.getChildren().map(x -> x.getData()).collect(Collectors.toList());
        TreeMap godchildren = godparent.getChildrenMap();
        TreeMap children = new TreeMap<>();
        godchildren.forEach((token, godchild) -> {
          try {
            long childCount = in.readVarLong();
            if (childCount > 0) {
              children.put(token, childCount);
              nodesRead.incrementAndGet();
            }
          } catch (IOException e) {
            throw new RuntimeException(e);
          }
        });
        node.writeChildren(children);
      });
    }

    return nodesRead.get();
  }
}