<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>

typedef struct TrieNode {
    bool isTerminal;
    std::map<char, TrieNode *> letters;
    std::string letter;

    TrieNode() { isTerminal = false; }
} TrieNode;

class Trie {
    TrieNode * root;

    std::string dfs(TrieNode * node) {
        std::vector<std::string> strings;
        for(auto &i : node->letters) if(i.second->isTerminal) { strings.push_back(dfs(i.second)); }
        if(strings.empty()) { return node->letter; }

        int index = 0;
        for(int i = 0; i < strings.size(); ++i) {
            if(strings[i].length() > strings[index].length()) index = i;
            if(strings[i].length() == strings[index].length()) index = strings[i] < strings[index] ? i : index;
        }

        return node->letter + strings[index];
    }

public:

    Trie() {
        root = new TrieNode();
    }
    
    void insert(string& word) {
        TrieNode * worked = root;
        for(auto &i : word) {
            auto find_node = worked->letters.find(i);
            if(find_node == worked->letters.end()) {
                TrieNode * newNode = new TrieNode();
                worked->letters.insert({i, newNode});
                worked = newNode;
                newNode->letter = i;
            } else {
                worked = find_node->second;
            }
        }
        worked->isTerminal = true;
    }

    std::string search() {
        TrieNode * worked = root;
        return dfs(worked);
    }
};

class Solution {
public:
    string longestWord(vector<string>& words) {
        Trie tree;
        for(auto &i : words) tree.insert(i);
        return tree.search();
    }
};
29784