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.

Solution:



Code:

public class Trie {
    class TrieNode {
        private TrieNode[] links;
        private int R = 26;
        private boolean isEnd;
        public TrieNode() {
            links = new TrieNode[R];
        }
        
        public boolean containsKey(char c) {
            return links[c - 'a'] != null;
        }
        
        public TrieNode get(char c) {
            return links[c - 'a'];
        }
        
        public void put(char c, TrieNode node) {
            links[c - 'a'] = node;
        }
        
        public void setEnd() {
            isEnd = true;
        }
        
        public boolean isEnd() {
            return isEnd;
        }
    }
    
    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 node = root;
        for (int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            if (!node.containsKey(c)) {
                node.put(c, new TrieNode());
            }
            node = node.get(c);
        }
        node.setEnd();
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode node = searchPrefix(word);
        return node != null && node.isEnd();
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode node = searchPrefix(prefix);
        return node != null;
    }
    
    public TrieNode searchPrefix(String word) {
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            if (node.containsKey(c)) {
                node = node.get(c);
            }
            else {
                return null;
            }
        }
        return node;
    }
}

/**
 * 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);
 */

public class Trie {

    class TrieNode {
        public TrieNode[] link;
        public boolean isEnd;
        public TrieNode() {
            this.link = new TrieNode[26];
            for (int i = 0; i < 26; i++) {
                this.link[i] = null;
            }
            this.isEnd = false;
        }
    }
    
    public TrieNode root;

    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode curr = root;
        for (char c : word.toCharArray()) {
            if (curr.link[c - 'a'] == null) {
                curr.link[c - 'a'] = new TrieNode();
            }
            curr = curr.link[c - 'a'];
        }
        curr.isEnd = true;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode curr = root;
        for (char c : word.toCharArray()) {
            if (curr.link[c - 'a'] == null) {
                return false;
            }
            else {
                curr = curr.link[c - 'a'];
            }
        }
        return curr.isEnd;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode curr = root;
        for (char c : prefix.toCharArray()) {
            if (curr.link[c - 'a'] == null) {
                return false;
            }
            else {
                curr = curr.link[c - 'a'];
            }
        }
        return true;
    }
}

/**
 * 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);
 */