LeetCode 211 Add and Search Word - Data structure design

题目描述

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") -> falsesearch("bad") -> truesearch(".ad") -> truesearch("b..") -> true

Note:
You may assume that all words are consist of lowercase letters a-z.

You should be familiar with how a Trie works. If not, please work on this problem: Implement Trie (Prefix Tree) first.

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分析

本题只能用Trie，但是……LeetCode最近加入了一个测试用例，我试了所有网上能找到的代码，都是Time Limit Exceeded！

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代码

    class TrieNode {        boolean isLeaf;        char c;        HashMap<Character, TrieNode> children = new HashMap<Character, TrieNode>();        // Initialize your data structure here.        public TrieNode() {        }        public TrieNode(char c) {            this.c = c;        }    }    public class WordDictionary {        private TrieNode root;        public WordDictionary() {            root = new TrieNode();        }        // Adds a word into the data structure.        public void addWord(String word) {            HashMap<Character, TrieNode> children = root.children;            for (int i = 0; i < word.length(); i++) {                char c = word.charAt(i);                TrieNode t;                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.isLeaf = 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 searchNode(word, root);        }        private boolean searchNode(String word, TrieNode t) {            if (t == null) {                return false;            }            if (word.length() == 0) {                return t.isLeaf;            }            HashMap<Character, TrieNode> children = t.children;            char c = word.charAt(0);            if (c == '.') {                for (char key : children.keySet()) {                    if (word.length() == 1 && children.get(key).isLeaf) {                        return true;                    }                    if (searchNode(word.substring(1), children.get(key))) {                        return true;                    }                }                return false;            } else if (!children.containsKey(c)) {                return false;            } else {                return searchNode(word.substring(1), children.get(c));            }        }    }    // Your WordDictionary object will be instantiated and called as such:    // WordDictionary wordDictionary = new WordDictionary();    // wordDictionary.addWord("word");    // wordDictionary.search("pattern");