<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:
     vector<TrieNode*> children;
     string mpWord;

     TrieNode() : mpWord(""), children(26, nullptr) {}
     ~TrieNode() {
         for (auto child : children)
             delete child;
     }
 };
class Solution {
public:
    string longestWord(vector<string>& words) {
        TrieNode* root = new TrieNode();
         for (string word : words) {
             TrieNode* node = root;
             for (char c : word) {
                 if(node->children[c - 'a'] == nullptr)
                    node->children[c - 'a'] = new TrieNode();
                 node = node->children[c - 'a'];
             }
             node->mpWord = word;
         }

         string ans;
         int maxLen = 0;
         for (string word : words) {
             TrieNode* node = root;
             bool bCandidate = true;
             for (char c : word) {
                 if (node->children[c - 'a']->mpWord=="") {
                     bCandidate = false;
                     break;
                 }
                 else
                     node = node->children[c - 'a'];
             }
             if (bCandidate) {
                 if (maxLen < word.length()) {
                     ans = word;
                     maxLen = word.length();
                 }
                 else if (maxLen == word.length() && ans > word)
                     ans = word;
             }
         }
         return ans;
    }
};
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