208. Implement Trie (Prefix Tree)

class TrieNode {
    public char val;
    public boolean isWord; 
    public TrieNode[] children = new TrieNode[26];
    public TrieNode() {}
    TrieNode(char c){
        TrieNode node = new TrieNode();
        node.val = c;
    }
}

public class Trie {
    private TrieNode root;
    public Trie() {
        root = new TrieNode();
        root.val = ' ';
    }

    public void insert(String word) {
        TrieNode ws = root;
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            if(ws.children[c - 'a'] == null){
                ws.children[c - 'a'] = new TrieNode(c);
            }
            ws = ws.children[c - 'a'];
        }
        ws.isWord = true;
    }

    public boolean search(String word) {
        TrieNode ws = root; 
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            if(ws.children[c - 'a'] == null) return false;
            ws = ws.children[c - 'a'];
        }
        return ws.isWord;
    }

    public boolean startsWith(String prefix) {
        TrieNode ws = root; 
        for(int i = 0; i < prefix.length(); i++){
            char c = prefix.charAt(i);
            if(ws.children[c - 'a'] == null) return false;
            ws = ws.children[c - 'a'];
        }
        return true;
    }
}

Runtime: 30 ms, faster than 78.71% of Java online submissions for Implement Trie (Prefix Tree).
Memory Usage: 48.9 MB, less than 63.08% of Java online submissions for Implement Trie (Prefix Tree).

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