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.

Solution

    class TrieNode {
        String val;
        Map<Character, TrieNode> map;

        public TrieNode() {
            val = null;
            map = new HashMap<>();
        }
    }

public class Trie {
    private TrieNode root;

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

    // Inserts a word into the trie.
    public void insert(String word) {
        insert(word, 0, root);
    }

    public void insert(String word, int d, TrieNode current) {
      if (word.length() == d) {
            current.val = word;
            return;
        }
        char currentChar = word.charAt(d);


        TrieNode next = null;
        if (current.map.containsKey(currentChar)) {
            next = current.map.get(currentChar);
        } else {
            next = new TrieNode();
            current.map.put(currentChar, next);
        }


        insert(word, d + 1, next);
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
        TrieNode runner = root;

        for (int i = 0; i < word.length(); i++) {
            runner = runner.map.get(word.charAt(i));
            if (runner == null) {
                return false;
            }
        }

        return runner.val == null ? false : runner.val.equals(word);
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
        TrieNode runner = root;

        for (int i = 0; i < prefix.length(); i++) {
            runner = runner.map.get(prefix.charAt(i));
            if (runner == null) {
                return false;
            }
        }

        return true;
    }
}

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