# 18. Trie

* search prefix

## 208. Implement Trie

* TrieNode class
* Trie class
  * insert, search, startsWith function

```java
class TrieNode{
    public TrieNode[] children;
    public boolean isWord;

    public TrieNode(){
        children = new TrieNode[26];
        isWord = false;
    }
}

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

    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode p = root;
        for(int i=0; i<word.length(); i++){
            int c = word.charAt(i)-'a';
            if(p.children[c] == null){
                p.children[c] = new TrieNode();
            }
            p = p.children[c];
        }
        p.isWord = true;
    }

    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode p = root;
        for(int i=0; i<word.length(); i++){
            int c = word.charAt(i)-'a';
            if(p.children[c] == null){
                return false;
            }
            p = p.children[c];
        }
        return p.isWord;
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode p = root;
        for(int i=0; i<prefix.length(); i++){
            int c = prefix.charAt(i)-'a';
            if(p.children[c] == null){
                return false;
            }
            p = p.children[c];
        }
        return true;
    }
}
```
