211. Add and Search Word - Data

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.
这题是Trie的基本操作。
我的经验是把Trie的操作提取出来，像这里面的 getOrCreate这个函数。
这样逻辑就简化很多了。
其它的就挺直接的这里就不多说了。

class WordDictionary {
    TrieNode root;
    /** Initialize your data structure here. */
    public WordDictionary() {
        root = new TrieNode('a');
    }
    
    /** Adds a word into the data structure. */
    public void addWord(String word) {
        TrieNode cur = root;
        for (char c : word.toCharArray()) {
            cur = cur.getOrCreate(c);
        }
        cur.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 helper(root, word, 0);
    }
    private boolean helper(TrieNode root, String word, int index) {
        if (root == null) return false;
        if (index == word.length()) {
            return root.isWord;
        }
        if (word.charAt(index) != '.') {
            return helper(root.get(word.charAt(index)), word, index + 1);
        } else {
            for (char c = 'a'; c <= 'z'; c++) {
                if (helper(root.get((char) c), word, index + 1)) return true;
            }
            return false;
        }
    }
}
class TrieNode {
    char c;
    boolean isWord;
    TrieNode[] child;
    public TrieNode(char c) {
        this.c = c;
        child = new TrieNode[26];
    }
    public TrieNode getOrCreate(char c) {
        if (child[c - 'a'] == null) {
            child[c - 'a'] = new TrieNode(c);
        }
        return get(c);
    }
    public TrieNode get(char c) {
        return child[c - 'a'];
    }
}