[LeetCode] 966. Vowel Spellchecker 元音拼寫檢查器

Given a wordlist, we want to implement a spellchecker that converts a query word into a correct word.

For a given query word, the spell checker handles two categories of spelling mistakes:

• Capitalization: If the query matches a word in the wordlist (case-insensitive), then the query word is returned with the same case as the case in the wordlist.
  • Example: wordlist = ["yellow"], query = "YellOw": correct = "yellow"
  • Example: wordlist = ["Yellow"], query = "yellow": correct = "Yellow"
  • Example: wordlist = ["yellow"], query = "yellow": correct = "yellow"
• Vowel Errors: If after replacing the vowels ('a', 'e', 'i', 'o', 'u') of the query word with any vowel individually, it matches a word in the wordlist (case-insensitive), then the query word is returned with the same case as the match in the wordlist.
  • Example: wordlist = ["YellOw"], query = "yollow": correct = "YellOw"
  • Example: wordlist = ["YellOw"], query = "yeellow": correct = "" (no match)
  • Example: wordlist = ["YellOw"], query = "yllw": correct = "" (no match)

In addition, the spell checker operates under the following precedence rules:

• When the query exactly matches a word in the wordlist (case-sensitive), you should return the same word back.
• When the query matches a word up to capitlization, you should return the first such match in the wordlist.
• When the query matches a word up to vowel errors, you should return the first such match in the wordlist.
• If the query has no matches in the wordlist, you should return the empty string.

Given some queries, return a list of words answer, where answer[i] is the correct word for query = queries[i].

Example 1:

Input: wordlist = ["KiTe","kite","hare","Hare"], queries = ["kite","Kite","KiTe","Hare","HARE","Hear","hear","keti","keet","keto"]
Output: ["kite","KiTe","KiTe","Hare","hare","","","KiTe","","KiTe"]

Note:

• 1 <= wordlist.length <= 5000
• 1 <= queries.length <= 5000
• 1 <= wordlist[i].length <= 7
• 1 <= queries[i].length <= 7
• All strings in wordlist and queries consist only of english letters.

這道題給了一組單詞，讓實現一個拼寫檢查器，把查詢單詞轉換成一個正確的單詞。這個拼寫檢查器主要有兩種功能，一種是可以忽略大小寫，另一種是忽略元音的錯誤，所謂元音是 a，e，i，o，u，這五個字母。另外題目中還制定了一些其他規則：假如有和查詢單詞一模一樣的單詞，考慮大小寫，此時應該優先返回。第二個優先級是字母及順序都一樣，但大小寫可能不同的，第三個優先級是有元音錯誤的單詞也可以返回，最后都不滿足的話返回空串。首先對於第一種情況，返回和查詢單詞一模一樣的單詞，很簡單，將所有單詞放入一個 HashSet 中，這樣就可以快速確定一個查詢單詞是否在原單詞數組中出現過。對於第二種情況，做法是將每個單詞都轉為小寫，然后建立小寫單詞和原單詞之間都映射，注意對於轉為小寫后相同都單詞，我們只映射第一個出現該小寫狀態的單詞，后面的不用管。對於第三種情況，對於每個單詞，轉為小寫之后，然后把所有的元音字母用特殊字符替代，比如下划線，然后也是建立這種特殊處理后的狀態和原單詞之間的映射。當映射都建立好了之后，就可以遍歷所有的查詢單詞了，首先是去 HashSet 中找，若有跟該查詢單詞一模一樣的，直接加入結果 res 中。若沒有，則先將查詢單詞變為小寫，然后去第一個 HashMap 中查找，若存在，直接加入結果 res 中。若沒有，再把所有的元音變為下划線，去第二個 HashMap 中查找，存在則直接加入結果 res 中。若沒有，則將空串加入結果 res 中，參見代碼如下：

解法一：

class Solution {
public:
    vector<string> spellchecker(vector<string>& wordlist, vector<string>& queries) {
        vector<string> res;
        unordered_set<string> st;
        unordered_map<string, string> m1;
        unordered_map<string, string> m2;
        for (int i = 0; i < wordlist.size(); ++i) {
            string word = wordlist[i];
            st.insert(word);
            transform(word.begin(), word.end(), word.begin(), ::tolower);
            if (!m1.count(word)) m1[word] = wordlist[i];
            for (char &c : word) {
                if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u') c = '_';
            }
            if (!m2.count(word)) m2[word] = wordlist[i];
        }
        for (string query : queries) {
            if (st.count(query)) {
                res.push_back(query);
                continue;
            }
            transform(query.begin(), query.end(), query.begin(), ::tolower);
            if (m1.count(query)) {
                res.push_back(m1[query]);
                continue;
            }
            for (char &c : query) {
                if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u') c = '_';
            }
            if (m2.count(query)) {
                res.push_back(m2[query]);
                continue;
            }
            res.push_back("");
        }
        return res;
    }
};

討論：這里博主不得不吐槽一下 C++ 的STL的功能實在不如 Java 強大，若用 Java 寫的話，可以直接調用 toLowerCase() 來轉小寫，同時可以用 replaceAll() 來快速替換元音，而 C++ 就顯得很笨拙了，哎，誰讓博主就是用 C++ 刷的順手呢～

Github 同步地址:

https://github.com/grandyang/leetcode/issues/966

參考資料：

https://leetcode.com/problems/vowel-spellchecker/

https://leetcode.com/problems/vowel-spellchecker/discuss/211189/JavaC%2B%2BPython-Two-HashMap

https://leetcode.com/problems/vowel-spellchecker/discuss/211238/C%2B%2B-Hash-Map-("Yellow"-"_yellow"-"y*ll*w")

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