<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>

class TrieNode {
public:
    bool isWord;
    string word;
    vector<TrieNode*> children;
    TrieNode() : isWord(false), children(26) {
    }
};

class Trie {
public:
    TrieNode* root;
    Trie() {
        root = new TrieNode();
    }
    void insert(const string& word) {
        TrieNode* curr = root;
        for (char c : word) {
            if (!curr->children[c - 'a'])
                curr->children[c - 'a'] = new TrieNode();
            curr = curr->children[c - 'a'];
        }
        curr->isWord = true;
        curr->word = word;
    }
    string search() {
        stack<TrieNode*> stk;
        stk.push(root);
        int maxLen = 0;
        string ans = "";
        while (!stk.empty()) {
            TrieNode* node = stk.top(); stk.pop();
            if (node->word.length() > maxLen) {
                maxLen = node->word.length();
                ans = node->word;
            }
            for (int i = 25; i >= 0; i--) {
                const auto& child = node->children[i];
                if (!child || !child->isWord) continue;
                stk.push(child);
            }
        }
        return ans;
    }
};

class Solution {
public:
    string longestWord(vector<string>& words) {
        return longestWord_Trie(words);
    }

    string longestWord_Trie(vector<string>& words) {
        Trie trie;
        for (const string& word : words)
            trie.insert(word);
        return trie.search();
    }
};
38284