<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 {
public:
    vector<string> split(const string& str) {
        vector<string> words;
        string word;
        for (char c : str) {
            if (c == ' ') {
                if (!word.empty()) {
                    words.push_back(word);
                    word.clear();
                }
            } else {
                word += c;
            }
        }
        if (!word.empty()) {
            words.push_back(word);
        }
        return words;
    }

    string replaceWords(vector<string>& dictionary, string sentence) {
        unordered_map<char, vector<string>> hashMap;

        for (const string& word : dictionary) {
            hashMap[word[0]].push_back(word);
        }

        for (auto& entry : hashMap) {
            sort(entry.second.begin(), entry.second.end(),
                 [](const string& a, const string& b) {
                     return a.size() < b.size();
                 });
        }

        vector<string> words = split(sentence);
        vector<string> resultWords;

        for (string& word : words) {
            char firstChar = word[0];
            bool replaced = false;

            if (hashMap.find(firstChar) != hashMap.end()) {
                for (const string& root : hashMap[firstChar]) {
                    if (word.substr(0, root.size()) == root) {
                        resultWords.push_back(root);
                        replaced = true;
                        break;
                    }
                }
            }

            if (!replaced) {
                resultWords.push_back(word);
            }
        }

        string result;
        for (size_t i = 0; i < resultWords.size(); ++i) {
            if (i > 0) {
                result += " ";
            }
            result += resultWords[i];
        }

        return result;
    }
};
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