leetcode 208. Implement Trie (Prefix Tree) 设计前缀树 ---------- java

Implement a trie with insert, search, and startsWith methods.

Note:
You may assume that all inputs are consist of lowercase letters a-z.

 

设计一个前缀树，包括insert,search,startsWith三种方法。

 

1、每个字母用一个Trie表示，同时isWord表示到目前Trie是否构成一个单词。

public class Trie {


    public char ch;
    public Trie[] nextTrie;
    public boolean isWord;
    
    /** Initialize your data structure here. */
    public Trie() {
        nextTrie = new Trie[26];
    }
    public Trie(char ch){
        this.ch = ch;
        nextTrie = new Trie[26];

    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        Trie[] nextTrie = this.nextTrie;
        for (int i = 0; i < word.length(); i++){
            int num = (int) (word.charAt(i) - 'a');
            if (nextTrie[num] == null){
                nextTrie[num] = new Trie(word.charAt(i));
            }
            if (i == word.length() - 1){
                nextTrie[num].isWord = true;
            }
            nextTrie = nextTrie[num].nextTrie;
        }
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        
        Trie[] nextTrie = this.nextTrie;
        for (int i = 0; i < word.length() - 1; i++){
            int num = (int) (word.charAt(i) - 'a');
            if (nextTrie[num] == null){
                return false;
            }
            nextTrie = nextTrie[num].nextTrie;
        }
        int num = (int) (word.charAt(word.length() - 1) - 'a');
        if (nextTrie[num] == null || nextTrie[num].isWord == false){
            return false;
        } else {
            return true;
        }
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String word) {
        Trie[] nextTrie = this.nextTrie;
        for (int i = 0; i < word.length(); i++){
            int num = (int) (word.charAt(i) - 'a');
            if (nextTrie[num] == null){
                return false;
            }
            nextTrie = nextTrie[num].nextTrie;
        }
        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);
 */