# 20200401

Design a data structure that supports the following two operations:

void addWord(word)
bool search(word)
search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.

Example:

addWord("bad")
addWord("dad")
addWord("mad")
search("pad") -> false
search("bad") -> true
search(".ad") -> true
search("b..") -> true
Note:
You may assume that all words are consist of lowercase letters a-z.

https://www.youtube.com/watch?v=AXjmTQ8LEoI

root
/ |
b d
/ |
a a
/ |
d d
(bad) (dad)
|
d
|
y
(daddy)

class WordDictionary {

    public class TrieNode {
        public TrieNode[] children = new TrieNode[26];
        public String item = "";
    }
    
    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.item = word;
    }
    
    /** 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 k, TrieNode node) {
        if (k == chs.length) return !node.item.equals("");   
        if (chs[k] != '.') {
            return node.children[chs[k] - 'a'] != null && match(chs, k + 1, node.children[chs[k] - 'a']);
        } else {
            for (int i = 0; i < node.children.length; i++) {
                if (node.children[i] != null) {
                    if (match(chs, k + 1, node.children[i])) {
                        return true;
                    }
                }
            }
        }
        return false;
    }
}

/**
 * Your WordDictionary object will be instantiated and called as such:
 * WordDictionary obj = new WordDictionary();
 * obj.addWord(word);
 * boolean param_2 = obj.search(word);
 */

 public class TrieNode {
        public TrieNode[] children = new TrieNode[26];
        public String item = "";
    }

            root
         /      |
        b       d
       /        |
      a         a
     /       |     \
    d        d      y
   (bad)     (dad)  (day)
             |
             d
             |
             y
             (daddy)

search: bad
search: ....(false)

match:(bad, 0, root)
match:(bad, 1, )

root
children: [null,TrieNode(b),null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null]
item: ""

children: [TrieNode(a),null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null]
item: ""

children: [null,null,null,TrieNode(d),null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null]
item: "bad"