更新

我觉得更好的是官方题解说的方法。 以下是我根据它写的。

题目

参考题解：

class Trie {
          
   
    class TrieNode{
          
   
        public int path;
        public int end;
        public HashMap<Character,TrieNode> next;
        public TrieNode(){
          
   
            path=0;
            end=0;
            next=new HashMap<>();
        }
    }
    private TrieNode root;
    public Trie() {
          
   
        root=new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
          
   
        if(word==null||word.length()==0)
            return;
        TrieNode node=root;
        for(int i=0;i<word.length();i++){
          
   
            Character c=(Character)word.charAt(i);
            if(!node.next.containsKey(c)){
          
   
                node.next.put(c,new TrieNode());
            }
            node=node.next.get(c);
            node.path++;
        }
        node.end++;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
          
   
        if(word==null||word.length()==0)
            return false;
        TrieNode node=root;
        for(int i=0;i<word.length();i++){
          
   
            Character c=(Character)word.charAt(i);
            if(!node.next.containsKey(c)){
          
   
                return false;
            }
            node=node.next.get(c);
        }
        if(node.end==0)
            return false;
        return true;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
          
   
        if(prefix==null||prefix.length()==0)
            return false;
        TrieNode node=root;
        for(int i=0;i<prefix.length();i++){
          
   
            Character c=(Character)prefix.charAt(i);
            if(!node.next.containsKey(c)){
          
   
                return false;
            }
            node=node.next.get(c);
        }
        return true;
    }
}

/**
 * Your Trie object will be instantiated and called as such:
 * Trie obj = new Trie();
 * obj.insert(word);
 * boolean param_2 = obj.search(word);
 * boolean param_3 = obj.startsWith(prefix);
 */
 
 /*
 public void delete(String word){
    if(word == null || word.equals("") || !search(word)) return ;
    TrieNode node = root;
    for (int i = 0; i < word.length(); i++) {
        char ch = word.charAt(i);
        if(--node.next.get(ch).path == 0){
            node.next.remove(ch);
            return;
        }
        node = node.next.get(ch);
    }
    node.end--;
}
 */

public void delete(String word){
          
   
    if(word == null || word.equals("") || !search(word)) return ;
    TrieNode node = root;
    for (int i = 0; i < word.length(); i++) {
          
   
        char ch = word.charAt(i);
        if(--node.next.get(ch).path == 0){
          
   
            node.next.remove(ch);
            return;
        }
        node = node.next.get(ch);
    }
    node.end--;
}