# Leetcode 208. Implement Trie (Prefix Tree)
###### tags: `Leetcode(JAVA)`

題目 : https://leetcode.com/problems/implement-trie-prefix-tree/ 。

想法 :

TRIE練習題。

時間複雜度 : O(n * l)。

程式碼 : (JAVA)

class Trie {

    class Node{
        Node[] child;
        boolean isEnd;
        Node(){
            child = new Node[26];
        }
    }
    
    Node root;
    public Trie() {
        root = new Node();
    }
    
    public void insert(String word) {
        Node curr = root;
        for(int i = 0 ; i < word.length() ; i++){
            char ch = word.charAt(i);
            if(curr.child[ch - 'a'] == null){
                curr.child[ch - 'a'] = new Node();
            }
            curr = curr.child[ch-'a'];
        }
        curr.isEnd = true;
    }
    
    public boolean search(String word) {
        Node curr = root;
        for(int i = 0 ; i < word.length() ; i++){
            char ch = word.charAt(i);
            if(curr.child[ch - 'a'] == null){
                return false;
            }
            curr = curr.child[ch - 'a'];
        }
        return curr.isEnd;
    }
    
    public boolean startsWith(String prefix) {
        Node curr = root;
        for(int i = 0 ; i < prefix.length() ; i++){
            char ch = prefix.charAt(i);
            if(curr.child[ch - 'a'] == null){
                return false;
            }
            curr = curr.child[ch - 'a'];
        }
        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);
 */