<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 Trie {
public:
    char val;
    Trie* children[26];
    bool isTerminal;
    Trie() {
        val = '-';
        isTerminal = false;
        for (int i = 0; i < 26; i++) {
            children[i] = NULL;
        }
    }
    Trie(char v) {
        val = v;
        isTerminal = false;
        for (int i = 0; i < 26; i++) {
            children[i] = NULL;
        }
    }

    void insert(string word) {
        if (word.length() == 0) {
            this->isTerminal = true;
            return;
        }
        char ch = word[0];
        int index = ch - 'a';
        Trie* child;
        if (this->children[index]) {
            child = this->children[index];
        } else {
            child = new Trie(ch);
            this->children[index] = child;
        }
        child->insert(word.substr(1));
    }

    bool searchUtil(string word, int& i) {
        if (this->isTerminal) {
            return true;
        }
        if (word.length() == 0) {
            return false;
        }

        char ch = word[0];
        int index = ch - 'a';
        Trie* child;
        if (this->children[index]) {
            child = this->children[index];
        } else {
            return false;
        }
        return child->searchUtil(word.substr(1), ++i);
    }

    int search(string word) {
        int i = 0;
        return searchUtil(word, i) ? i : -1;
        
    }

    bool startsWith(string prefix) {
        if (prefix.length() == 0) {
            return true;
        }
        char ch = prefix[0];
        int index = ch - 'a';
        Trie* child;
        if (this->children[index]) {
            child = this->children[index];
        } else {
            return false;
        }
        return child->startsWith(prefix.substr(1));
    }
};

class Solution {
public:
    string replaceWords(vector<string>& dictionary, string sentence) {
        Trie* trie = new Trie();
        // creating a trie index
        for (auto it : dictionary) {
            trie->insert(it);
        }

        // replacing the  words

        int start = 0, end = 0;
        string ans = "";
        while (end < sentence.size()) {
          
            if (sentence[end] == ' ' || end == sentence.size() - 1) {
                int len =
                    end == sentence.size() - 1 ? sentence.size() : end - start;
                string word = sentence.substr(start, len);
                int trieIndex = trie->search(word);
                ans += trieIndex != -1 ? word.substr(0, trieIndex ) : word;
                if (sentence[end] == ' ') {
                    ans += " ";
                }
                start = end + 1;
            }
            ++end;
        }
        return ans;
    }
};
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