Longest Word in Dictionary
<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>
Trie; Array; Hash Table; String; Sorting
type Trie struct {
	children [26]*Trie
	isEnd    bool
}

func (t *Trie) insert(w string) {
	node := t
	for i := 0; i < len(w); i++ {
		idx := w[i] - 'a'
		if node.children[idx] == nil {
			node.children[idx] = &Trie{}
		}
		node = node.children[idx]
	}
	node.isEnd = true
}

func (t *Trie) search(w string) bool {
	node := t
	for i := 0; i < len(w); i++ {
		idx := w[i] - 'a'
		if node.children[idx] == nil || !node.children[idx].isEnd {
			return false
		}
		node = node.children[idx]
	}
	return true
}

func longestWord(words []string) string {
	trie := &Trie{}
	for _, w := range words {
		trie.insert(w)
	}

	ans := ""
	for _, w := range words {
		if trie.search(w) && (len(ans) < len(w) || (len(ans) == len(w) && w < ans)) {
			ans = w
		}
	}
	return ans
}
