<Trie> 208 211

208. Implement Trie (Prefix Tree)

class TrieNode{
    private char val;
    public boolean isWord;
    public TrieNode[] children = new TrieNode[26];
    public TrieNode(){};
    public TrieNode(char c){
        this.val = c;
    }
}
class Trie {
    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 cur = root;
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            if(cur.children[c - 'a'] == null){
                cur.children[c - 'a'] = new TrieNode(c);
            }
            cur = cur.children[c - 'a'];
        }
        cur.isWord = true;
    }

    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode cur = root;
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            if(cur.children[c - 'a'] == null) return false;
            cur = cur.children[c - 'a'];
        }
        return cur.isWord;
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode cur = root;
        for(int i = 0; i < prefix.length(); i++){
            char c =prefix.charAt(i);
            if(cur.children[c - 'a'] == null) return false;
            cur = cur.children[c - 'a'];
        }
        return true;
    }
}

211. Add and Search Word - Data structure design

class WordDictionary {

    public class TrieNode{
        public TrieNode[] children = new TrieNode[26];
        public boolean isWord;
    }

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

    }

    /** Adds a word into the data structure. */
    public void addWord(String word) {
        TrieNode node = root;
        for(char c : word.toCharArray()){
            if(node.children[c - 'a'] == null){
                node.children[c - 'a'] = new TrieNode();
            }
            node = node.children[c - 'a'];
        }
        node.isWord = true;
    }

    /** Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter. */
    public boolean search(String word) {
        return match(word.toCharArray(), 0, root);
    }

    private boolean match(char[] chs, int start, TrieNode node){
        if(start == chs.length) return node.isWord;

        if(chs[start] == '.'){
            for(int i = 0; i < node.children.length; i++){
                if(node.children[i] != null && match(chs, start + 1, node.children[i]))
                    return true;
            }
        }else{
            return node.children[chs[start] - 'a'] != null && match(chs, start + 1, node.children[chs[start] - 'a']);
        }
    return false;
    }
}