Add and Search Word - Data structure design (M)

題目

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.

題意

設計一個數據結構，支援插入單詞和搜尋單詞兩個操作。其中，搜尋單詞的引數可以是一個包含萬用字元"."的正則。

思路

和 0208. Implement Trie (Prefix Tree) (M) 一樣使用字典樹。不同之處在於當搜尋字元為"."時，要查詢所有出現過的字母。

程式碼實現

Java

class WordDictionary {
    Node root;

    /** Initialize your data structure here. */
    public WordDictionary() {
        root = new Node();
    }

    /** Adds a word into the data structure. */
    public void addWord(String word) {
        Node p = root;
        for (char c : word.toCharArray()) {
            if (p.children[c - 'a'] == null) {
                p.children[c - 'a'] = new Node();
            }
            p = p.children[c - 'a'];
        }
        p.end = 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 search(word, 0, root);
    }

    private boolean search(String word, int index, Node p) {
        if (index == word.length()) {
            return p.end;
        }

        char c = word.charAt(index);
        if (c == '.') {
            for (Node next : p.children) {
                if (next != null && search(word, index + 1, next)) {
                    return true;
                }
            }
            return false;
        } else {
            return p.children[c - 'a'] != null ? search(word, index + 1, p.children[c - 'a']) : false;
        }
    }
}

class Node {
    Node[] children = new Node[26];
    boolean end;
}

/**
 * Your WordDictionary object will be instantiated and called as such:
 * WordDictionary obj = new WordDictionary(); obj.addWord(word); boolean param_2
 * = obj.search(word);
 */