<p>In English, we have a concept called <strong>root</strong>, which can be followed by some other word to form another longer word - let&#39;s call this word <strong>derivative</strong>. For example, when the <strong>root</strong> <code>&quot;help&quot;</code> is followed by the word <code>&quot;ful&quot;</code>, we can form a derivative <code>&quot;helpful&quot;</code>.</p>

<p>Given a <code>dictionary</code> consisting of many <strong>roots</strong> and a <code>sentence</code> consisting of words separated by spaces, replace all the derivatives in the sentence with the <strong>root</strong> forming it. If a derivative can be replaced by more than one <strong>root</strong>, replace it with the <strong>root</strong> that has <strong>the shortest length</strong>.</p>

<p>Return <em>the <code>sentence</code></em> after the replacement.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> dictionary = [&quot;cat&quot;,&quot;bat&quot;,&quot;rat&quot;], sentence = &quot;the cattle was rattled by the battery&quot;
<strong>Output:</strong> &quot;the cat was rat by the bat&quot;
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> dictionary = [&quot;a&quot;,&quot;b&quot;,&quot;c&quot;], sentence = &quot;aadsfasf absbs bbab cadsfafs&quot;
<strong>Output:</strong> &quot;a a b c&quot;
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= dictionary.length &lt;= 1000</code></li>
	<li><code>1 &lt;= dictionary[i].length &lt;= 100</code></li>
	<li><code>dictionary[i]</code> consists of only lower-case letters.</li>
	<li><code>1 &lt;= sentence.length &lt;= 10<sup>6</sup></code></li>
	<li><code>sentence</code> consists of only lower-case letters and spaces.</li>
	<li>The number of words in <code>sentence</code> is in the range <code>[1, 1000]</code></li>
	<li>The length of each word in <code>sentence</code> is in the range <code>[1, 1000]</code></li>
	<li>Every two consecutive words in <code>sentence</code> will be separated by exactly one space.</li>
	<li><code>sentence</code> does not have leading or trailing spaces.</li>
</ul>

class Solution {
    class Trie {
    public:
        struct Node {
            char ch;
            vector<Node*> children;
            bool isEnd;

            Node(char ch, vector<Node*> children, bool isEnd) {
                this->ch = ch;
                this->children = children;
                this->isEnd = isEnd;
            }
        };
        Node* head;
        Trie() { head = new Node('/', vector<Node*>(26, NULL), false); }

        void insert(string word) {
            Node* temp = head;
            for (int i = 0; i < word.size(); i++) {
                char c = word[i];
                if (temp->children[c - 'a'] == NULL) {
                    temp->children[c - 'a'] =
                        new Node(c, vector<Node*>(26), false);
                }
                if (i == word.size() - 1)
                    temp->children[c - 'a']->isEnd = true;
                temp = temp->children[c - 'a'];
            }
        }

        string search(string word) {
            Node* temp = head;
            string prefix = "";
            for (int i = 0; i < word.size(); i++) {
                char c = word[i];
                if (temp->children[c - 'a'] == NULL)
                    return "";
                temp = temp->children[c - 'a'];
                prefix += c;
                if (temp->isEnd)
                    return prefix;
            }
            return "";
        }
    };

public:
    string replaceWords(vector<string>& dictionary, string sentence) {
        Trie* trie = new Trie();
        for (string dict : dictionary)
            trie->insert(dict);
        string ans = "";
        string word = "";
        for (int i = 0; i < sentence.size(); i++) {
            if (sentence[i] == ' ') {
                string newWord = trie->search(word);
                if (newWord == "")
                    ans += word + ' ';
                else
                    ans += newWord + ' ';
                word = "";
            } else
                word += sentence[i];
        }
        string newWord = trie->search(word);
        if (newWord == "")
            ans += word;
        else
            ans += newWord;
        return ans;
    }
};
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