Tree [trees] trie Trie

Thanks Modifying Code in Columbia crush on a data structure , the classic of classics.
Thanks Modifying Code in Columbia crush on a data structure , the classic of classics.
Thanks Modifying Code in Columbia crush on a data structure , the classic of classics.

Trie Profile

Trie also called a trie , prefix tree (the Prefix Tree) , trie
Trie search string efficiency is mainly related with the length of the string

Advantages: efficiency of major search prefix with prefix length about the
shortcomings: the need to consume a lot of memory , so there is room for improvement

Example:
Assuming Trie store cat, dog, doggy, does, cast, add six words

Trie achieve

Interface Design

public interface Trie <V> {
	int size(); 
	boolean isEmpty(); 
	void clear(); 
	boolean contains(String str); 
	V add(String str,V value); 
	V remove(String str); 
	boolean starswith(String prefix);
}

Source

/**
 * @author yusael
 * Trie 字典树
 */
public class Trie <V> {
	private int size;
	private Node<V> root;
	
	private static class Node<V>{
		Node<V> parent;
		HashMap<Character, Node<V>> children;
		Character character; // 为删除做准备
		V value;
		boolean word; // 是否为单词的结尾(是否位一个完整的单词)
		public Node(Node<V> parent) {
			this.parent = parent;
		}
	}
	
	public int size(){
		return size;
	}
	
	public boolean isEmpty(){
		return size == 0;
	}
	
	public void clear(){
		size = 0;
		root = null;
	}
	
	public V get(String key){
		Node<V> node = node(key);
		return (node!=null && node.word) ? node.value : null;
	}
	
	public boolean contains(String key){
		Node<V> node = node(key);
		return node!=null && node.word;
	}
	
	public V add(String key, V value){
		keyCheck(key);
		
		// 创建根节点
		if(root == null){
			root = new Node<>(null);
		}
		
		Node<V> node = root;
		int len = key.length();
		for(int i = 0; i < len; i++){
			char c = key.charAt(i);
			boolean emptyChildren = (node.children==null);
			Node<V> childNode = emptyChildren ? null : node.children.get(c);
			if(childNode == null){
				childNode = new Node<>(node);
				childNode.character = c;
				node.children = emptyChildren ? new HashMap<>() : node.children;
				node.children.put(c, childNode);
			}
			node = childNode;
		}
		
		if(node.word){ // 已经存在这个单词
			V oldValue = node.value;
			node.value = value;
			return oldValue;
		}
		
		// 新增一个单词
		node.word = true;
		node.value = value;
		size++;
		return null;
	}
	
	public V remove(String key){
		// 找到最后一个节点
		Node<V> node = node(key);
		// 如果不是单词结尾，不用作任何处理
		if(node==null || !node.word) return null;
		size--;
		V oldValue = node.value;
			
		// 如果还有子节点
		if(node.children!=null && !node.children.isEmpty()){
			node.word = false;
			node.value = null;
			return oldValue; 
		}
		
		// 没有子节点
		Node<V> parent = null;
		while((parent = node.parent) != null){
			parent.children.remove(node.character);
			if(parent.word || !parent.children.isEmpty()) break;
			node = parent;
		}
		return oldValue;
	}
	
	public boolean startsWith(String prefix){
		return node(prefix) != null;
	}
	
	/**
	 * 根据传入字符串，找到最后一个节点
	 * 例如输入 dog
	 * 找到 g
	 */
	private Node<V> node(String key){
		keyCheck(key);
		
		Node<V> node = root;
		int len = key.length();
		for(int i = 0; i < len; i++){
			if(node==null || node.children==null || node.children.isEmpty()) return null;
			char c = key.charAt(i);
			node = node.children.get(c);
		}
		return node;
	}
	
	private void keyCheck(String key){
		if(key==null || key.length()==0){
			throw new IllegalArgumentException("key must not be empty");
		}
	}
	
}

test

public class Main {
	public static void main(String[] args) {
		Trie<Integer> trie = new Trie<>();
		trie.add("cat", 1);
		trie.add("dog", 2);
		trie.add("catalog", 3);
		trie.add("cast", 4);
		trie.add("小码哥", 5);
		System.out.println(trie.size() == 5);
		System.out.println(trie.startsWith("do"));
		System.out.println(trie.startsWith("c"));
		System.out.println(trie.startsWith("ca"));
		System.out.println(trie.startsWith("cat"));
		System.out.println(trie.startsWith("cata"));
		System.out.println(!trie.startsWith("hehe"));
		System.out.println(trie.get("小码哥") == 5);
		System.out.println(trie.remove("cat") == 1);
		System.out.println(trie.remove("catalog") == 3);
		System.out.println(trie.remove("cast") == 4);
		System.out.println(trie.size() == 2);
		System.out.println(trie.startsWith("小"));
		System.out.println(trie.startsWith("do"));
		System.out.println(!trie.startsWith("c"));
	}
}