208 Implement Trie (Prefix Tree)

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https://leetcode.com/problems/implement-trie-prefix-tree/discuss/58832

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

    /** Inserts a word into the trie. */
    // O(m), m is the key length
    public void insert(String word) {
        TrieNode node = root;
        for(int i = 0; i < word.length(); i++){
            char currentChar = word.charAt(i);
            if(!node.containsKey(currentChar)){
                node.put(currentChar, new TrieNode());
            }
            node = node.get(currentChar);
        }
        node.setEnd();
    }

    // search a prefix or whole key in trie and
    // returns the node where search ends
    private TrieNode searchPrefix(String prefix){
        TrieNode node = root;
        for(int i = 0; i < prefix.length(); i++){
            char currentLetter = prefix.charAt(i);
            if(node.containsKey(currentLetter)){
                node = node.get(currentLetter);
            }
            else{
                return null;
            }
        }
        return node;
    }
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode node =searchPrefix(word);
        if(node != null && node.isEnd()){
            return true;
        }
        else{
            return false;
        }
    }

    /** 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;
    }
}

class TrieNode{
    private TrieNode[] links;
    private final int R = 26;
    public boolean isEnd;
    public int cnt = 0;

    public TrieNode(){
        links = new TrieNode[R];
    }

    public boolean containsKey(char ch){
        return links[ch - 'a'] != null;
    }

    public TrieNode get(char ch){
        return links[ch - 'a'];
    } 

    public void put(char ch, TrieNode node){
        links[ch - 'a'] = node;
    }

    public void setEnd(){
        isEnd = true;
    }
    public boolean isEnd(){
        return isEnd;
    }
}



/**
 * 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);
 */