<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 Trie {
    struct Node {
        bool isWord = false;
        array<Node*, 26> children{};
        ~Node() {
            for (auto child : children) {
                delete child;
            }
        }
    };

    Node *root;

public:
    Trie() : root(new Node) {}

    Trie(vector<string> &words) : Trie() {
        for (auto word : words) {
            insert(word);
        }
    }

    void insert(string &word) {
        auto cur = root;
        for (auto c : word) {
            int idx = c - 'a';
            if (!cur->children[idx]) {
                cur->children[idx] = new Node;
            }
            cur = cur->children[idx];
        }
        cur->isWord = true;
    }

    string getLongestWord() {
        string ans;
        string word;
        search_(root, word, ans);
        return ans;
    }

private:
    void search_(Node *cur, string &word, string &ans) {
        for (int i = 0; i < 26; i++) {
            auto child = cur->children[i];
            if (child && child->isWord) {
                word.push_back('a' + i);
                if (word.length() > ans.length()) {
                    ans = word;
                }
                search_(child, word, ans);
                word.pop_back();
            }
        }
    }
};

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