208. 实现 Trie (前缀树)

class Trie:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.children = [None] * 26
        self.is_end = False

    def insert(self, word: str) -> None:
        """
        Inserts a word into the trie.
        """
        node = self
        for c in word:
            index = ord(c) - ord("a")
            if node.children[index] is None:
                node.children[index] = Trie()
            node = node.children[index]
        node.is_end = True

    def search(self, word: str) -> bool:
        """
        Returns if the word is in the trie.
        """
        node = self._search_prefix(word)
        return node is not None and node.is_end

    def startsWith(self, prefix: str) -> bool:
        """
        Returns if there is any word in the trie that starts with the given prefix.
        """
        node = self._search_prefix(prefix)
        return node is not None

    def _search_prefix(self, prefix: str):
        node = self
        for c in prefix:
            index = ord(c) - ord("a")
            if node.children[index] is None:
                return None
            node = node.children[index]
        return node

# Your Trie object will be instantiated and called as such:
# obj = Trie()
# obj.insert(word)
# param_2 = obj.search(word)
# param_3 = obj.startsWith(prefix)

class Trie {
    private Trie[] children;
    private boolean isEnd;

    /** Initialize your data structure here. */
    public Trie() {
        children = new Trie[26];
        isEnd = false;
    }

    /** Inserts a word into the trie. */
    public void insert(String word) {
        Trie node = this;
        for (int i = 0; i < word.length(); ++i) {
            char c = word.charAt(i);
            int index = c - 'a';
            if (node.children[index] == null) {
                node.children[index] = new Trie();
            }
            node = node.children[index];
        }
        node.isEnd = true;
    }

    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        Trie node = searchPrefix(word);
        return node != null && node.isEnd;
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        Trie node = searchPrefix(prefix);
        return node != null;
    }

    private Trie searchPrefix(String prefix) {
        Trie node = this;
        for (int i = 0; i < prefix.length(); ++i) {
            char c = prefix.charAt(i);
            int index = c - 'a';
            if (node.children[index] == null) {
                return null;
            }
            node = node.children[index];
        }
        return node;
    }
}

/**
 * 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);
 */

/**
 * Initialize your data structure here.
 */
var Trie = function() {
    this.children = {};
};

/**
 * Inserts a word into the trie. 
 * @param {string} word
 * @return {void}
 */
Trie.prototype.insert = function(word) {
    let node = this.children;
    for (let char of word) {
        if (!node[char]) {
            node[char] = {};
        }
        node = node[char];
    }
    node.isEnd = true;
};

/**
 * Returns if the word is in the trie. 
 * @param {string} word
 * @return {boolean}
 */
Trie.prototype.search = function(word) {
    let node = this.searchPrefix(word);
    return node != undefined && node.isEnd != undefined;
};

Trie.prototype.searchPrefix = function (prefix) {
    let node = this.children;
    for (let char of prefix) {
        if (!node[char]) return false;
        node = node[char];
    }
    return node;
}

/**
 * Returns if there is any word in the trie that starts with the given prefix. 
 * @param {string} prefix
 * @return {boolean}
 */
Trie.prototype.startsWith = function(prefix) {
    return this.searchPrefix(prefix);
};

/**
 * Your Trie object will be instantiated and called as such:
 * var obj = new Trie()
 * obj.insert(word)
 * var param_2 = obj.search(word)
 * var param_3 = obj.startsWith(prefix)
 */