208. 实现 Trie (前缀树)

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

    public Trie() {
        this.children = new Trie[26];
        this.isEnd = false;
    }
    
    public void insert(String word) {
        Trie node = this;
        for (int i = 0; i < word.length(); ++i) {
            char c = word.charAt(i);
            if (node.children[c - 'a'] == null) {
                node.children[c - 'a'] = new Trie();
            }
            node = node.children[c - 'a'];
            // if (i == word.length() - 1) node.children[c - 'a'].isEnd = true;
        }
        node.isEnd = true;
    }
    
    public boolean search(String word) {
        Trie node = searchPrefix(word);
        return node != null && node.isEnd;
    }
    
    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);
            if (node.children[c - 'a'] == null) return null;
            node = node.children[c - 'a'];
        }
        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);
 */