手撸 算法 java 字典树算法

 字典树，又称单词查找树，是一个典型的一对多的字符串匹配算法。“一”指的是一个模式串，“多”指的是多个模板串。字典树经常被用来统计、排序和保存大量的字符串。它利用字符串的公共前缀来减少查询时间，最大限度地减少无谓的字符串比较；并可以减少存储量；

package tire;
import java.util.TreeMap;
public class Tire {

  private class Node {
    public boolean isWord = false;
    TreeMap<Character, Node> next;

    public Node() {
      next = new TreeMap<>();
    }
  }

  public Node root;
  public int size;

  public Tire() {
    root = new Node();
    size = 0;
  }

  public void add(String words) {//添加一个节点
    add(root, words, 0);
  }

  public void add(Node preNode, String words, int index) {
    if (words.length() == index) {// 递归到底的情况
      if (preNode.isWord == false)
        size++;
      preNode.isWord = true;
      return;
    }

    // 判断当前是否已经存在;
    Character c = words.charAt(index);
    // 当前根是否已经存在指向下一个字符的节点
    if (preNode.next.get(c) == null) {
      preNode.next.put(c, new Node());
    }

    add(preNode.next.get(c), words, index+1);// 不存在的话添加一个新节点
  }

  public boolean searchChar(String words) {
    Node node = root;
    for (int i = 0; i < words.length(); i++) {
      Character c = words.charAt(i);
      if (null == node.next.get(c)) {
        return false;
      }  

      node = node.next.get(c);
    }

    return node.isWord;
  }

  public boolean containsPreFix(String words)
  {
    Node node = root;
    int len = words.length();
    for(int i =0;i<len;i++)
    {
      Character c = words.charAt(i);
      node = node.next.get(c);
      if(null ==node)
      {
        return false;
      }
      
    }
    return true;
  }
  /**
   * @param args
   */
  public static void main(String[] args) {
    // TODO Auto-generated method stub

    Tire tire = new Tire();
    tire.add("apple");
    tire.add("hello");
    
    tire.add("quickly");
    
    System.out.println("word search:"+tire.searchChar("word"));
    System.out.println("word search:"+tire.searchChar("hello"));
    
  }

}