211. Add and Search Word - Data structure design

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.

Solution

字典树的典型应用场景
1. 字典树Node的定义
2. item存在的意义:识别在路径中,但却没有定义过的情况

Complexity

Code

class WordDictionary {

    class TrieNode{
        TrieNode[] children = new TrieNode[26];
        String item = "";
    }
    
    private TrieNode root;
    /** Initialize your data structure here. */
    public WordDictionary() {
        root = new TrieNode();
    }
    
    /** Adds a word into the data structure. */
    public void addWord(String word) {
        TrieNode node = root;
        for(Character 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);
    }
    
    public boolean match(char[] arr, int k, TrieNode node){
        if(k == arr.length){
            return !node.item.equals("");
        }
            
        if(arr[k] == '.'){
            for(int i = 0; i < node.children.length;i++){
                if(node.children[i] != null && match(arr, k+1, node.children[i]))
                    return true;
            }
        }else{
            return node.children[arr[k]-'a'] != null && match(arr, k+1, node.children[arr[k]-'a']);
        }
        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);
 */