<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>


#include <queue>
#include <string>
#include <vector>



class Solution {
public:
    std::string longestWord(std::vector<std::string>& words) {
		Node root;

		for (auto& word : words) {
			Node *node = &root;

			for (char c : word) {
				if (node->child.empty())
					node->child.resize(26);

				node = &node->child[25 - (c - 'a')];
			}

			node->is_word = true;
			node->word = &word;
		}

		std::string *result = NULL;
		std::queue<Node *> queue;

		queue.push(&root);

		while (!queue.empty()) {
			for (auto& node : queue.front()->child) {
				if (node.is_word) {
					queue.push(&node);
					result = node.word;
				}
			}

			queue.pop();
		}

		return result ? *result : "";
    }

private:
	struct Node {
		bool is_word = false;
		std::string *word = NULL;
		std::vector<Node> child;
	};
};
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