<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>

#include <iostream>
#include <string>

class TrieNode{

public:
    TrieNode * children[26];
    bool word_end;
    TrieNode(){
        word_end = false;
        for(int i = 0; i < 26; i++){
            children[i] = NULL;
        }
    }
};

void insertKey(TrieNode * root, const string & key){
    TrieNode * curr = root;
    for(char c:key){
        if(curr->children[c - 'a'] == NULL){
            TrieNode * new_node = new TrieNode();
            curr->children[c - 'a'] = new_node;
        }
        curr = curr->children[c - 'a'];
    }
    curr->word_end = true;  
}

bool findKey(TrieNode * root, const string & key){
    TrieNode * curr = root;
    for(char c:key){
        if(curr->children[c - 'a'] == NULL){
            return false;
        }
        curr = curr->children[c - 'a'];
    }
    return curr->word_end;  
}

string findRoot(TrieNode * root, const string & word){
    TrieNode * curr = root;
    string word_root;

    for(char c:word){
        if(curr->children[c - 'a'] == NULL){
            return word; // root is itself
        }
        word_root +=c ;
        if(curr->children[c - 'a']->word_end){
            return word_root; // root is itself
        }
        curr = curr->children[c - 'a'];
    }
    return word_root;  
}

class Solution {

private:


vector<string> getWords(string s){
    vector<string> res;

    int pos = s.find(" ");;
    while(pos != std::string::npos){
        res.push_back(s.substr(0, pos));
        s.erase(0, pos + 1); // 3 is the length of the delimiter, " "
        pos = s.find(" ");
    }
    // add last word:
    res.push_back(s);
    return res;
}




public:
    string replaceWords(vector<string>& dictionary, string sentence) {
        
        string roots;
        vector<string> words = getWords(sentence);

        //dictionary to TRIE
        TrieNode root = TrieNode();
        for(string key:dictionary){
            //cout<<key<<endl;
            insertKey(&root, key);
        }

        for (auto word:words) {
            //cout<<"word:"<<word<<endl;
            roots = roots + findRoot(&root, word) + ' ';
        }
        //remove last space
        roots = roots.substr(0, roots.size() - 1);
        return roots;
    }
};
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