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https://leetcode.com/problems/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.
For 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.
解题思路：
这题实际上是 Implement Trie (Prefix Tree) 的follow-up。有了上一题的设计，这题唯一需要解决的，就是search这个方法，当遇到‘.‘的时候，如何办。
本题的addword()方法中，是没有‘.‘的，所以Trie树内肯定没有‘.‘。那么当遇到‘.‘的时候，只要递归search下一层次的所有子节点，有一个路径里找到，就返回true，否则立刻返回false。
public class WordDictionary { class TrieNode { // Initialize your data structure here. boolean isWord; Map<Character, TrieNode> next; public TrieNode() { next = new HashMap<Character, TrieNode>(); isWord = false; } } private TrieNode root; public WordDictionary() { root = new TrieNode(); } // Adds a word into the data structure. public void addWord(String word) { TrieNode cur = root; for(int i = 0; i < word.length(); i++) { if(cur.next.get(word.charAt(i)) == null) { TrieNode next = new TrieNode(); cur.next.put(word.charAt(i), next); } cur = cur.next.get(word.charAt(i)); } 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 searchHelper(root, word); } public boolean searchHelper(TrieNode cur, String word) { if(cur == null) { return false; } for(int i = 0; i < word.length(); i++) { if(word.charAt(i) != ‘.‘) { cur = cur.next.get(word.charAt(i)); } else { for(TrieNode value : cur.next.values()) { if(searchHelper(value, word.substring(i + 1))) { return true; } } return false; } if(cur == null) { return false; } } return cur.isWord; } } // Your WordDictionary object will be instantiated and called as such: // WordDictionary wordDictionary = new WordDictionary(); // wordDictionary.addWord("word"); // wordDictionary.search("pattern");
Add and Search Word - Data structure design
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原文地址：http://www.cnblogs.com/NickyYe/p/4606027.html
