leetcode 211. Add and Search Word - Data structure design 字典树的简单应用

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(){};
}