208.Implement Trie (Prefix Tree)

Implement a trie withinsert,search, andstartsWithmethods.

Example:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // returns true
trie.search("app");     // returns false
trie.startsWith("app"); // returns true
trie.insert("app");   
trie.search("app");     // returns true

class Trie {
    class TrieNode {
        int count;
        List<String> list;
        TrieNode[] children;
        TrieNode() {
            count = 0;
            list = new ArrayList<>();
            children = new TrieNode[26];
        }
    }

    private TrieNode root;
    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }

    /** Inserts a word into the trie. */
    public void insert(String word) {
        if (word == null) return;
        TrieNode node = root;
        for (char c : word.toCharArray()) {
            if (node.children[c-'a'] == null) {
                node.children[c-'a'] = new TrieNode();
            }
            node = node.children[c-'a'];
            node.count++;
        }
        node.list.add(word);
    }

    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        if (word == null) return false;
        TrieNode node = root;
        for (char c : word.toCharArray()) {
            node = node.children[c-'a'];
            if (node == null || node.count == 0) return false;
        }
        return node != null && node.list.contains(word);
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        if (prefix == null) return false;
        TrieNode node = root;
        for (char c : prefix.toCharArray()) {
            node = node.children[c-'a'];
            if (node == null || node.count == 0) return false;
        }
        return node != null && node.count != 0;        
    }
}

/**
 * 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);
 */