<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>

struct TrieNode{
    TrieNode* children[26];
    int index;
    TrieNode(){
        for(int i=0;i<26;++i)children[i]=NULL;
        index=-1;
    }
};
void insert(TrieNode* ptr,string& s,int ind){
    int len=s.size();
    for(int i=0;i<len;++i){
        if(!ptr->children[s[i]-'a']){
            ptr->children[s[i]-'a']=new TrieNode();
        }
        ptr=ptr->children[s[i]-'a'];
    }
    ptr->index=ind;
}
class Solution {
public:
    string replaceWords(vector<string>& dictionary, string sentence) {
        // Trie  
        TrieNode* root=new TrieNode();
        int n=dictionary.size();
        for(int i=0;i<n;++i){
            insert(root,dictionary[i],i);
        }
        int m=sentence.size();
        string res="";
        string word="";
        TrieNode* ptr=root;
        int flag=0;
        for(int i=0;i<m;++i){
            if(sentence[i]==' '){
                if(flag!=1){
                    res+=word;
                    res+=" ";
                }
                ptr=root;
                flag=0;
                word="";
                continue;
            }
            if(flag==0){
                if(ptr->children[sentence[i]-'a']){
                    ptr=ptr->children[sentence[i]-'a'];
                    if(ptr->index!=-1){
                        res+=dictionary[ptr->index];
                        res+=" ";
                        flag=1;
                    }
                }else{
                    flag=2;
                }
                word.push_back(sentence[i]);
            }else if(flag==2){
                word.push_back(sentence[i]);
            }
        }
        if(flag!=1)res+=word;
        if(res.back()==' ')res.pop_back();
        return res;
    }
};
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