208. Implement Trie (Prefix Tree)

Implement a trie with insert, search, and startsWith methods.

Note:
You may assume that all inputs are consist of lowercase letters a-z.

class TrieNode {
    public TrieNode[] Child {get;set;}
    public bool EndWord {get;set;}
    // Initialize your data structure here.
    public TrieNode() {
        Child = new TrieNode[26];
        EndWord = false;
    }
}

public class Trie {
    private TrieNode root;

    public Trie() {
        root = new TrieNode();
    }

    // Inserts a word into the trie.
    public void Insert(String word) {
        var sentinel = root;
        for(int i =0;i<word.Length;i++)
        {
            if(sentinel.Child[word[i]-'a'] == null) sentinel.Child[word[i]-'a'] = new TrieNode();
            sentinel = sentinel.Child[word[i]-'a'];
        }
        sentinel.EndWord = true;
    }

    // Returns if the word is in the trie.
    public bool Search(string word) {
         var sentinel = root;
         for(int i =0;i<word.Length;i++)
        {
             if(sentinel.Child[word[i]-'a'] == null) return false;
             sentinel = sentinel.Child[word[i]-'a'];
        }
        return sentinel.EndWord;
        
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public bool StartsWith(string word) {
         var sentinel = root;
         for(int i =0;i<word.Length;i++)
        {
             if(sentinel.Child[word[i]-'a'] == null) return false;
             sentinel = sentinel.Child[word[i]-'a'];
        }
        return true;
    }
}

// Your Trie object will be instantiated and called as such:
// Trie trie = new Trie();
// trie.Insert("somestring");
// trie.Search("key");