<p>Given an array of strings <code>words</code> representing an English Dictionary, return <em>the longest word in</em> <code>words</code> <em>that can be built one character at a time by other words in</em> <code>words</code>.</p>

<p>If there is more than one possible answer, return the longest word with the smallest lexicographical order. If there is no answer, return the empty string.</p>

<p>Note that the word should be built from left to right with each additional character being added to the end of a previous word.&nbsp;</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> words = [&quot;w&quot;,&quot;wo&quot;,&quot;wor&quot;,&quot;worl&quot;,&quot;world&quot;]
<strong>Output:</strong> &quot;world&quot;
<strong>Explanation:</strong> The word &quot;world&quot; can be built one character at a time by &quot;w&quot;, &quot;wo&quot;, &quot;wor&quot;, and &quot;worl&quot;.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> words = [&quot;a&quot;,&quot;banana&quot;,&quot;app&quot;,&quot;appl&quot;,&quot;ap&quot;,&quot;apply&quot;,&quot;apple&quot;]
<strong>Output:</strong> &quot;apple&quot;
<strong>Explanation:</strong> Both &quot;apply&quot; and &quot;apple&quot; can be built from other words in the dictionary. However, &quot;apple&quot; is lexicographically smaller than &quot;apply&quot;.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= words.length &lt;= 1000</code></li>
	<li><code>1 &lt;= words[i].length &lt;= 30</code></li>
	<li><code>words[i]</code> consists of lowercase English letters.</li>
</ul>

struct Node
{
    Node* links[26];
    bool flag = false;

    bool containsKey(char ch)
    {
        return links[ch - 'a'] != NULL;
    }

    Node* get(char ch)
    {
        return links[ch - 'a'];
    }

    void put(char ch, Node* node)
    {
        links[ch - 'a'] = node;
    }

    void setEnd()
    {
        flag = true;
    }

    bool retuFlag()
    {
        return flag;
    }
};

class Trie
{
private:
    Node* root;
public:
    Trie()
    {
        root = new Node();
    }

    void insert(string &word)
    {
        Node* node = root;

        for(int i = 0;i < word.size();i++)
        {
            if(!node->containsKey(word[i]))
            node->put(word[i], new Node());

            node = node->get(word[i]);
        }
        node->setEnd();
    }

    bool checkPrefixExist(string &word)
    {
        Node* node = root;

        for(auto &it:word)
        {
            if(!node->containsKey(it))
            return false;
            else
            {
                node = node->get(it);
                if(!node->retuFlag())
                return false;
            }
        }

        return true;
    }
};

class Solution {
public:
    string longestWord(vector<string>& words) 
    {
        Trie trie;

        for(auto &it:words)
        trie.insert(it);

        string ans = "";
        for(auto &it:words)
        {
            if(trie.checkPrefixExist(it))
            {
                if(it.size() > ans.size())
                ans = it;
                else if(it.size() == ans.size())
                ans = ans > it ? it : ans;
            }
        }

        return ans;
    }
};
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