LeetCode 648（C＃）

题目

在英语中，我们有一个叫做 词根(root) 的概念，可以词根后面添加其他一些词组成另一个较长的单词——我们称这个词为 继承词(successor)。例如，词根an，跟随着单词 other(其他)，可以形成新的单词 another(另一个)。

现在，给定一个由许多词根组成的词典 dictionary 和一个用空格分隔单词形成的句子 sentence。你需要将句子中的所有继承词用词根替换掉。如果继承词有许多可以形成它的词根，则用最短的词根替换它。

你需要输出替换之后的句子。

示例 1：
输入：dictionary = [“cat”,“bat”,“rat”], sentence = “the cattle was rattled by the battery”
输出：“the cat was rat by the bat”

示例 2：
输入：dictionary = [“a”,“b”,“c”], sentence = “aadsfasf absbs bbab cadsfafs”
输出：“a a b c”

代码

• 正则表达式

using System.Text.RegularExpressions;

public class Solution 
{
    
    public string ReplaceWords(IList<string> dictionary, string sentence) 
    {
    
        foreach (var dic in dictionary)
        {
    
            string regex = @$"((?<= )({
      dic})\w+|^({
      dic})\w+)";
            sentence = Regex.Replace(sentence, regex, dic);
        }

        return sentence;
    }
}

• 哈希枚举

public class Solution 
{
    
    public string ReplaceWords(IList<string> dictionary, string sentence) 
    {
    
        ISet<string> set = new HashSet<string>();
        foreach (var dic in dictionary)
            set.Add(dic);
        
        string[] words = sentence.Split(" ");
        for (int i = 0; i < words.Length; i++)
        {
    
            string word = words[i];
            for (int j = 0; j < word.Length - 1; j++)
            {
    
                if (set.Contains(word[0..(j + 1)]))
                {
    
                    words[i] = word[0..(j + 1)];
                    break;
                }
            }
        }

        return string.Join(" ", words);
    }
}

• 前缀树

public class Solution 
{
    
    private Trie _root = new Trie();

    public string ReplaceWords(IList<string> dictionary, string sentence) 
    {
    
        foreach (var s in dictionary) Add(s);
        
        StringBuilder sb = new StringBuilder();
        foreach (var s in sentence.Split(" "))
            sb.Append(Query(s)).Append(" ");

        sb.Length = sb.Length - 1;
        return sb.ToString();
    }

    private void Add(string s)
    {
    
        Trie p = _root;
        for (int i = 0; i < s.Length; i++)
        {
    
            int u = s[i] - 'a';
            if (p.childer[u] == null)
                p.childer[u] = new Trie();
            p = p.childer[u]; 
        }
        p.isEnd = true;
    }

    private string Query(string s)
    {
    
        Trie p = _root;
        for (int i = 0; i < s.Length; i++)
        {
    
            int u = s[i] - 'a';
            if (p.childer[u] == null) break;
            if (p.childer[u].isEnd) return s[0..(i + 1)];
            p = p.childer[u];
        }

        return s;
    }

    private class Trie
    {
    
        public bool isEnd;
        public Trie[] childer = new Trie[26];
    }
}