題目描述：
In English, we have a concept called root, which can be followed by some other word to form another longer word – let’s call this word successor. For example, when the root "an" is followed by the successor word "other", we can form a new word "another".
Given a dictionary consisting of many roots and a sentence consisting of words separated by spaces, replace all the successors in the sentence with the root forming it. If a successor can be replaced by more than one root, replace it with the root that has the shortest length.
Return the sentence after the replacement.
Example 1:
Input: dictionary = ["cat","bat","rat"], sentence = "the cattle was rattled by the battery"
Output: "the cat was rat by the bat"
Example 2:
Input: dictionary = ["a","b","c"], sentence = "aadsfasf absbs bbab cadsfafs"
Output: "a a b c"
Example 3:
Input: dictionary = ["a", "aa", "aaa", "aaaa"], sentence = "a aa a aaaa aaa aaa aaa aaaaaa bbb baba ababa"
Output: "a a a a a a a a bbb baba a"
Example 4:
Input: dictionary = ["catt","cat","bat","rat"], sentence = "the cattle was rattled by the battery"
Output: "the cat was rat by the bat"
Example 5:
Input: dictionary = ["ac","ab"], sentence = "it is abnormal that this solution is accepted"
Output: "it is ab that this solution is ac"
Constraints:
1 <= dictionary.length <= 10001 <= dictionary[i].length <= 100dictionary[i]consists of only lower-case letters.1 <= sentence.length <= 10^6sentenceconsists of only lower-case letters and spaces.The number of words in
sentenceis in the range[1, 1000]The length of each word in
sentenceis in the range[1, 1000]Each two consecutive words in
sentencewill be separated by exactly one space.sentencedoes not have leading or trailing spaces.
一刷題解（Trie）：
這題給了我們一個「字根」列表，還有一個句子字符串，要我們在這個句子中找出所有通過「字根 + 一些字母」組成的單詞，然後將這些單詞用字根取代。對此，我們需要兩步工序：
第一步，將字根裡的字符串放到一個字首樹中，構造一個包含了所有指定字根的字首樹。
第二步，把字首樹構建完成後，再對句子中的每個單詞進行遍歷，檢查這些單詞是否包含字首樹中所記錄的字符。如果包含，則代表單詞是由字根或字根+一些字母所組成的，那就可以用字根將其取代，如果不包含，那就直接進入下一個單詞的檢查中。
public class Solution {
public string ReplaceWords(IList<string> dictionary, string sentence) {
//Pass 1: 根據root構建字首樹
TrieNode rootNode = new TrieNode();
foreach(string root in dictionary)
{
TrieNode curr = rootNode;
foreach(char c in root.ToCharArray())
{
if(curr.children[c - 'a'] == null) { curr.children[c - 'a'] = new TrieNode(); }
curr = curr.children[c - 'a'];
}
curr.word = root;
}
StringBuilder sb = new StringBuilder();
string[] words = sentence.Split(' ');
//Pass 2: 遍歷句子中的所有字符串，檢查是否包含root
foreach(string word in words)
{
if(sb.Length > 0) { sb.Append(" "); } //如果加過了一個元素，每次遍歷前先加一個空格
TrieNode curr = rootNode; //遍歷字首樹
//遍歷每個字符串中的所有字符
foreach(char c in word.ToCharArray())
{
//字符與root之間有出入 || 遍歷到root的底部（curr.word != null）
if(curr.children[c - 'a'] == null || curr.word != null) { break; }
//移動到下個節點
curr = curr.children[c - 'a'];
}
//如果字符串與不包含root，直接返回原字符，否則就使用root取代原字符
sb.Append(curr.word == null ? word : curr.word);
}
return sb.ToString();
}
}
public class TrieNode
{
public TrieNode[] children = new TrieNode[26];
public string word = null;
}