<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:
    string replaceWords(vector<string>& dictionary, string sentence) {
        sort(dictionary.begin(), dictionary.end(), [&](auto const& a, auto const& b) {
            return a.size() < b.size();
        });
        
        vector<string> words;
        size_t spaceIndex = sentence.find(" "), start = 0;
        while(spaceIndex != string::npos) {
            words.push_back(sentence.substr(start, spaceIndex - start));
            start = spaceIndex + 1;
            spaceIndex = sentence.find(" ", start);
        }
        words.push_back(sentence.substr(start));

        string ans;
        unordered_map<string, string> m;
        for(int i = 0; i < words.size(); i++) {
            string word = words[i];
            string replacement = word;
            if(m.find(word) != m.end()) {
                replacement = m[word];
            } else {
                for(string root : dictionary) {
                    if(replacement.find(root) == 0) {
                        replacement = root;
                        break;
                    }
                }
                m[word] = replacement;
            }
            ans += replacement;
            if(i != words.size() - 1)
                ans += " ";
        }

        return ans;
    }
};
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