[LeetCode] 211. Add and Search Word - Data structure design

轉自LeetCode

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>

這題可以看成是 208. Implement Trie (Prefix Tree) 的衍生題

主要想法差不多，唯一比較不一樣的地方是，這次搜尋的可以用萬用字元 .

想法如下

• 如果沒遇到萬用字元，那麼就是正常歷遍 Prefix Tree 來找

• 如果遇到萬用字元，那麼歷遍當下 node 所有可連接的節點，並配合 dfs 的方式來找

code 如下

Java

	class WordDictionary {
	private TrieNode mRoot;
	/** Initialize your data structure here. */
	public WordDictionary() {
	mRoot = new TrieNode();
	}
	/** Adds a word into the data structure. */
	public void addWord(String word) {
	TrieNode node = mRoot;
	for(final char c : word.toCharArray()) {
	if(!node.containsKey(c)) {
	node.put(c, new TrieNode());
	}
	node = node.get(c);
	}
	node.setEnd();
	}
	/** 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 dfs(mRoot, word);
	}
	private boolean dfs(final TrieNode startNode, final String word) {
	final int len = word.length();
	TrieNode node = startNode;
	char c;
	for(int i = 0; i < len; i++) {
	c = word.charAt(i);
	if(c != '.' && node != null) {
	node = node.get(c);
	}
	else if(c == '.' && node != null) {
	for(int j = 0; j < 26; j++) {
	if(dfs(node.get((char)('a' + j)), word.substring(i+1))) {
	return true;
	}
	}
	return false;
	}
	else {
	break;
	}
	}
	return node != null && node.isEnd();
	}
	}
	class TrieNode {
	private static final int LEN = 26;
	private TrieNode[] mList;
	private boolean mIsEnd;
	public TrieNode() {
	mList = new TrieNode[26];
	mIsEnd = false;
	}
	public void setEnd() {
	mIsEnd = true;
	}
	public boolean isEnd() {
	return mIsEnd;
	}
	public void put(final char key, final TrieNode node) {
	mList[key - 'a'] = node;
	}
	public TrieNode get(final char key) {
	return mList[key - 'a'];
	}
	public boolean containsKey(final char key) {
	return mList[key - 'a'] != null;
	}
	}
	/**
	* Your WordDictionary object will be instantiated and called as such:
	* WordDictionary obj = new WordDictionary();
	* obj.addWord(word);
	* boolean param_2 = obj.search(word);
	*/

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