208. 实现 Trie (前缀树) (JAVA)

实现一个 Trie (前缀树)，包含 insert, search, 和 startsWith 这三个操作。

示例:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple"); // 返回 true
trie.search("app"); // 返回 false
trie.startsWith("app"); // 返回 true
trie.insert("app");
trie.search("app"); // 返回 true
说明:

你可以假设所有的输入都是由小写字母 a-z 构成的。
保证所有输入均为非空字符串。

 

 

class Trie {

    /** Initialize your data structure here. */
    public Trie() {
        root = new TreeNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TreeNode current = root;
        for(int i = 0; i < word.length(); i++){
            if(current.value[word.charAt(i)-'a'] == null) {
                current.value[word.charAt(i)-'a'] = new TreeNode();
            }
            current = current.value[word.charAt(i)-'a'];
        }
        current.isEnd = true;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        if(!startsWith(word)){
            return false;
        }
        if(current.isEnd){
            return true;
        } else {
            return false;
        }
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        current = root;
        for(int i = 0; i < prefix.length(); i++){
            if(current.value[prefix.charAt(i)-'a'] == null) {
                return false;
            }
            current = current.value[prefix.charAt(i)-'a'];
        }
        return true;
    }

    public class TreeNode {
        public TreeNode[] value;
        public boolean isEnd;

        public TreeNode() {
            this.value = new TreeNode[26];
            this.isEnd = false;
        }
    }

    private TreeNode root;
    private TreeNode current;
}

/**
 * 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);
 */