leetcode 211. Add and Search Word

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.

For example:

addWord(“bad”)
addWord(“dad”)
addWord(“mad”)
search(“pad”) -> false
search(“bad”) -> true
search(“.ad”) -> true
search(“b..”) -> true

这道题和leetcode 208. Implement Trie (Prefix Tree) 字典树的构造 基本一样，不过在搜索的过程中使用了DFS深度优先遍历，字典树应该记住。

代码如下：

public class WordDictionary {    private TrieNode root = new TrieNode();    public void addWord(String word)     {        Map<Character, TrieNode> children = root.children;        for(int i=0; i<word.length(); i++)        {            char c = word.charAt(i);            TrieNode t=null;            if(children.containsKey(c))                t = children.get(c);            else             {                t = new TrieNode(c);                children.put(c, t);            }            children = t.children;            if(i==word.length()-1)                t.leaf=true;        }    }    public boolean search(String word)     {        return searchNode(word, root);    }    /*     * 递归搜索     *      * */    public boolean searchNode(String word, TrieNode tn)     {        if(tn==null)             return false;        if(word.length() == 0 )            return tn.leaf;        Map<Character, TrieNode> children = tn.children;        TrieNode t = null;        char c = word.charAt(0);        if(c=='.')         {            for(char key : children.keySet() )             {                if(searchNode(word.substring(1), children.get(key) ))                     return true;            }            return false;        } else if(!children.containsKey(c))             return false;        else         {            t = children.get(c);            return searchNode(word.substring(1), t);        }    }    }class TrieNode {    // Initialize your data structure here.    char c;    boolean leaf;    HashMap<Character, TrieNode> children = new HashMap<Character, TrieNode>();    public TrieNode(char c)     {        this.c = c;    }        public TrieNode(){};}